text:
What is the longest checkmate problem a human has composed?
Well, I looked at some long checkmates, and I wonder, what is the longest checkmate a human has composed?

The longest known checkmate problem composed by a human is dependent on a few criteria that are generally used by chess composers. Namely, it is a question of whether or not you want the problem to have a unique solution, meaning that there is only one possible solution with Black defending optimally, and if you want the position to be legal or not, meaning that it is reachable from the starting position. Another consideration is whether or not promoted pieces are allowed, as most composers try to not use them. Finally, it is also debatable whether or not an illegal position must have only pieces from the chess box, with pawns being converted as needed.
Here is a selection of a few problems that fall along these lines.
This is the longest legal problem with a unique solution and no promoted pieces.
[Title "Walther Jørgensen, Thema Danicum 1982, Mate In 226"]
[fen "1N2Q3/p6n/p5n1/p1p2rpb/p4k1r/K1P4p/2PP4/6B1 w - - 0 1"]

1. Bh2+! Kf3 2. Qe3+ Kg2 3. Qg1+ Kf3 4. Qf1+ Kg4 5. Qe2+ Rf3 6. Qe6+ Rf5 7. Nd7 Kf3 8. Qe3+ Kg2 9. Qg1+ Kf3 10. Qf1+ Kg4 11. Qe2+ Rf3 12. Qe6+ Rf5 13. Kb2! Kf3 14. Qe3+ Kg2 15. Qg1+ Kf3 16. Qf1+ Kg4 17. Qe2+ Rf3 18. Qe6+ Rf5 19. Kc1! Kf3 20. Qe3+ Kg2 21. Qg1+ Kf3 22. Qf1+ Kg4 23. Qe2+ Rf3 24. Qe6+ Rf5 25. Kd1! a3! 26. Kc1 Kf3 27. Qe3+ Kg2 28. Qg1+ Kf3 29. Qf1+ Kg4 30. Qe2+ Rf3 31. Qe6+ Rf5 32. Kb1 Kf3 33. Qe3+ Kg2 34. Qg1+ Kf3 35. Qf1+ Kg4 36. Qe2+ Rf3 37. Qe6+ Rf5 38. Ka2 Kf3 39. Qe3+ Kg2 40. Qg1+ Kf3 41. Qf1+ Kg4 42. Qe2+ Rf3 43. Qe6+ Rf5 44. Kxa3 Kf3 45. Qe3+ Kg2 46. Qg1+ Kf3 47. Qf1+ Kg4 48. Qe2+ Rf3 49. Qe6+ Rf5 50. Kb2 Kf3 51. Qe3+ Kg2 52. Qg1+ Kf3 53. Qf1+ Kg4 54. Qe2+ Rf3 55. Qe6+ Rf5 56. Kc1 Kf3 57. Qe3+ Kg2 58. Qg1+ Kf3 59. Qf1+ Kg4 60. Qe2+ Rf3 61. Qe6+ Rf5 62. Kd1 a4! 63. Kc1 Kf3 64. Qe3+ Kg2 65. Qg1+ Kf3 66. Qf1+ Kg4 67. Qe2+ Rf3 68. Qe6+ Rf5 69. Kd1 a5! 70. Kc1 Kf3 71. Qe3+ Kg2 72. Qg1+ Kf3 73. Qf1+ Kg4 74. Qe2+ Rf3 75. Qe6+ Rf5 76. Kd1 a6! 77. Kc1 Kf3 78. Qe3+ Kg2 79. Qg1+ Kf3 80. Qf1+ Kg4 81. Qe2+ Rf3 82. Qe6+ Rf5 83. Kd1 a3 84. Kc1 Kf3 85. Qe3+ Kg2 86. Qg1+ Kf3 87. Qf1+ Kg4 88. Qe2+ Rf3 89. Qe6+ Rf5 90. Kb1 Kf3 91. Qe3+ Kg2 92. Qg1+ Kf3 93. Qf1+ Kg4 94. Qe2+ Rf3 95. Qe6+ Rf5 96. Ka2 Kf3 97. Qe3+ Kg2 98. Qg1+ Kf3 99. Qf1+ Kg4 100. Qe2+ Rf3 101. Qe6+ Rf5 102. Kxa3 Kf3 103. Qe3+ Kg2 104. Qg1+ Kf3 105. Qf1+ Kg4 106. Qe2+ Rf3 107. Qe6+ Rf5 108. Kb2 Kf3 109. Qe3+ Kg2 110. Qg1+ Kf3 111. Qf1+ Kg4 112. Qe2+ Rf3 113. Qe6+ Rf5 114. Kc1 Kf3 115. Qe3+ Kg2 116. Qg1+ Kf3 117. Qf1+ Kg4 118. Qe2+ Rf3 119. Qe6+ Rf5 120. Kd1 a4! 121. Kc1 Kf3 122. Qe3+ Kg2 123. Qg1+ Kf3 124. Qf1+ Kg4 125. Qe2+ Rf3 126. Qe6+ Rf5 127. Kd1 a5! 128. Kc1 Kf3 129. Qe3+ Kg2 130. Qg1+ Kf3 131. Qf1+ Kg4 132. Qe2+ Rf3 133. Qe6+ Rf5 134. Kd1 a3 135. Kc1 Kf3 136. Qe3+ Kg2 137. Qg1+ Kf3 138. Qf1+ Kg4 139. Qe2+ Rf3 140. Qe6+ Rf5 141. Kb1 Kf3 142. Qe3+ Kg2 143. Qg1+ Kf3 144. Qf1+ Kg4 145. Qe2+ Rf3 146. Qe6+ Rf5 147. Ka2 Kf3 148. Qe3+ Kg2 149. Qg1+ Kf3 150. Qf1+ Kg4 151. Qe2+ Rf3 152. Qe6+ Rf5 153. Kxa3 Kf3 154. Qe3+ Kg2 155. Qg1+ Kf3 156. Qf1+ Kg4 157. Qe2+ Rf3 158. Qe6+ Rf5 159. Kb2 Kf3 160. Qe3+ Kg2 161. Qg1+ Kf3 162. Qf1+ Kg4 163. Qe2+ Rf3 164. Qe6+ Rf5 165. Kc1 Kf3 166. Qe3+ Kg2 167. Qg1+ Kf3 168. Qf1+ Kg4 169. Qe2+ Rf3 170. Qe6+ Rf5 171. Kd1 a4 172. Kc1 Kf3 173. Qe3+ Kg2 174. Qg1+ Kf3 175. Qf1+ Kg4 176. Qe2+ Rf3 177. Qe6+ Rf5 178. Kd1 c4! 179. Kc1 Kf3 180. Qe3+ Kg2 181. Qg1+ Kf3 182. Qf1+ Ke4! 183. Qxc4+ Kf3 184. Qf1+ Kg4 185. Qe2+ Rf3 186. Qe6+ Rf5 187. Kd1 a3 188. Kc1 Kf3 189. Qe3+ Kg2 190. Qg1+ Kf3 191. Qf1+ Kg4 192. Qe2+ Rf3 193. Qe6+ Rf5 194. Kb1 Kf3 195. Qe3+ Kg2 196. Qg1+ Kf3 197. Qf1+ Kg4 198. Qe2+ Rf3 199. Qe6+ Rf5 200. Ka2 Kf3 201. Qe3+ Kg2 202. Qg1+ Kf3 203. Qf1+ Kg4 204. Qe2+ Rf3 205. Qe6+ Rf5 206. Kxa3 Kf3 207. Qe3+ Kg2 208. Qg1+ Kf3 209. Qf1+ Kg4 210. Qe2+ Rf3 211. Qe6+ Rf5 212. Kb2 Kf3 213. Qe3+ Kg2 214. Qg1+ Kf3 215. Qf1+ Kg4 216. Qe2+ Rf3 217. Qe6+ Rf5 218. Kc1 Kf3 219. Qe3+ Kg2 220. Qg1+ Kf3 221. Qf1+ Kg4 222. Qe2+ Rf3 223. Qe6+ Rf5 224. Kd1 Nf8,Nf6 225. Nf6+ Kf3 226. Qe2#

Based off of an earlier mate in 292 with an illegal position, this mate in 257 has as legal position with some minor duals in the solution.
[Title "Ottó Titusz Bláthy, Vielzügige Schachaufg 1889, Mate In 257 Legal Version of the #292"]
[FEN "q5nn/1pk1p3/p3P1p1/P3rpP1/1Kp1pP1p/8/2PQ1PP1/8 w - - 0 1"]

1. Qd7+ Kb8 2. Qd8+ Ka7 3. Qd4+ Rc5 4. Qxc5+ Kb8 5. Qe5+ Kc8 6. Qd5 Kc7 7. Qd7+ Kb8 8. Qd8+ Ka7 9. Qb6+ Kb8 10. c3 Kc8 11. Qc5+ Kb8 12. Qe5+ Kc8 13. Qd5 Kc7 14. Qd7+ Kb8 15. Qd8+ Ka7 16. Qb6+ Kb8 17. Ka3 Kc8 18. Qc5+ Kb8 19. Qe5+ Kc8 20. Qd5 Kc7 21. Qd7+ Kb8 22. Qd8+ Ka7 23. Qb6+ Kb8 24. Kb2 Kc8 25. Qc5+ Kb8 26. Qe5+ Kc8 27. Qd5 Kc7 28. Qd7+ Kb8 29. Qd8+ Ka7 30. Qb6+ Kb8 31. Kc1 Kc8 32. Qc5+ Kb8 33. Qe5+ Kc8 34. Qd5 Kc7 35. Qd7+ Kb8 36. Qd8+ Ka7 37. Qb6+ Kb8 38. Kd1 Kc8 39. Qc5+ Kb8 40. Qe5+ Kc8 41. Qd5 Kc7 42. Qd7+ Kb8 43. Qd8+ Ka7 44. Qb6+ Kb8 45. Ke2 Kc8 46. Qc5+ Kb8 47. Qe5+ Kc8 48. Qd5 Kc7 49. Qd7+ Kb8 50. Qd8+ Ka7 51. Qb6+ Kb8 52. Kf1 Kc8 53. Qc5+ Kb8 54. Qe5+ Kc8 55. Qd5 Kc7 56. Qd7+ Kb8 57. Qd8+ Ka7 58. Qb6+ Kb8 59. Kg1 Kc8 60. Qc5+ Kb8 61. Qe5+ Kc8 62. Qd5 Kc7 63. Qd7+ Kb8 64. Qd8+ Ka7 65. Qb6+ Kb8 66. Kh2 Kc8 67. Qc5+ Kb8 68. Qe5+ Kc8 69. Qd5 Kc7 70. Qd7+ Kb8 71. Qd8+ Ka7 72. Qb6+ Kb8 73. Kh3 Kc8 74. Qc5+ Kb8 75. Qe5+ Kc8 76. Qd5 Kc7 77. Qd7+ Kb8 78. Qd8+ Ka7 79. Qb6+ Kb8 80. Kxh4 Kc8 81. Qc5+ Kb8 82. Qe5+ Kc8 83. Qd5 Kc7 84. Qd7+ Kb8 85. Qd8+ Ka7 86. Qb6+ Kb8 87. Kh3 Kc8 88. Qc5+ Kb8 89. Qe5+ Kc8 90. Qd5 Kc7 91. Qd7+ Kb8 92. Qd8+ Ka7 93. Qb6+ Kb8 94. Kh2 Kc8 95. Qc5+ Kb8 96. Qe5+ Kc8 97. Qd5 Kc7 98. Qd7+ Kb8 99. Qd8+ Ka7 100. Qb6+ Kb8 101. Kg1 Kc8 102. Qc5+ Kb8 103. Qe5+ Kc8 104. Qd5 Kc7 105. Qd7+ Kb8 106. Qd8+ Ka7 107. Qb6+ Kb8 108. Kf1 Kc8 109. Qc5+ Kb8 110. Qe5+ Kc8 111. Qd5 Kc7 112. Qd7+ Kb8 113. Qd8+ Ka7 114. Qb6+ Kb8 115. Ke2 Kc8 116. Qc5+ Kb8 117. Qe5+ Kc8 118. Qd5 Kc7 119. Qd7+ Kb8 120. Qd8+ Ka7 121. Qb6+ Kb8 122. Kd1 Kc8 123. Qc5+ Kb8 124. Qe5+ Kc8 125. Qd5 Kc7 126. Qd7+ Kb8 127. Qd8+ Ka7 128. Qb6+ Kb8 129. Kc1 Kc8 130. Qc5+ Kb8 131. Qe5+ Kc8 132. Qd5 Kc7 133. Qd7+ Kb8 134. Qd8+ Ka7 135. Qb6+ Kb8 136. Kb2 Kc8 137. Qc5+ Kb8 138. Qe5+ Kc8 139. Qd5 Kc7 140. Qd7+ Kb8 141. Qd8+ Ka7 142. Qb6+ Kb8 143. Ka3 Kc8 144. Qc5+ Kb8 145. Qe5+ Kc8 146. Qd5 Kc7 147. Qd7+ Kb8 148. Qd8+ Ka7 149. Qb6+ Kb8 150. Kb4 Kc8 151. Qc5+ Kb8 152. Qe5+ Ka7 153. Qd4+ Kb8 154. Qxh8 Kc7 155. Qe5+ Kc8 156. Qd5 Kb8 157. Qd8+ Ka7 158. Qb6+ Kb8 159. Ka3 Kc8 160. Qc5+ Kb8 161. Qe5+ Kc8 162. Qd5 Kc7 163. Qd7+ Kb8 164. Qd8+ Ka7 165. Qb6+ Kb8 166. Kb2 Kc8 167. Qc5+ Kb8 168. Qe5+ Kc8 169. Qd5 Kc7 170. Qd7+ Kb8 171. Qd8+ Ka7 172. Qb6+ Kb8 173. Kc1 Kc8 174. Qc5+ Kb8 175. Qe5+ Kc8 176. Qd5 Kc7 177. Qd7+ Kb8 178. Qd8+ Ka7 179. Qb6+ Kb8 180. Kd1 Kc8 181. Qc5+ Kb8 182. Qe5+ Kc8 183. Qd5 Kc7 184. Qd7+ Kb8 185. Qd8+ Ka7 186. Qb6+ Kb8 187. Ke2 Kc8 188. Qc5+ Kb8 189. Qe5+ Kc8 190. Qd5 Kc7 191. Qd7+ Kb8 192. Qd8+ Ka7 193. Qb6+ Kb8 194. Kf1 Kc8 195. Qc5+ Kb8 196. Qe5+ Kc8 197. Qd5 Kc7 198. Qd7+ Kb8 199. Qd8+ Ka7 200. Qb6+ Kb8 201. Kg1 Kc8 202. Qc5+ Kb8 203. Qe5+ Kc8 204.Qd5 Kc7 205. Qd7+ Kb8 206. Qd8+ Ka7 207. Qb6+ Kb8 208. Kh2 Kc8 209. Qc5+ Kb8 210. Qe5+ Kc8 211. Qd5 Kc7 212. Qd7+ Kb8 213. Qd8+ Ka7 214. Qb6+ Kb8 215. Kh3 Kc8 216. Qc5+ Kb8 217. Qe5+ Kc8 218. Qd5 Kc7 219. Qd7+ Kb8 220. Qd8+ Ka7 221. Qb6+ Kb8 222. g4 Kc8 223. Qc5+ Kb8 224. Qe5+ Kc8 225. Qd5 Kc7 226. Qd7+ Kb8 227. Qd8+ Ka7 228. Qb6+ Kb8 229. gxf5 gxf5 230. Kh4 Kc8 231. Qc5+ Kb8 232. Qe5+ Kc8 233. Qd5 Kc7 234. Qd7+ Kb8 235. Qd8+ Ka7 236. Qb6+ Kb8 237. Kh5 Kc8 238. Qc5+ Kb8 239. Qe5+ Kc8 240. Qd5 Kc7 241. Qd7+ Kb8 242. Qd8+ Ka7 243. Qb6+ Kb8 244. Kg6 Kc8 245. Qc5+ Kb8 246. Qe5+ Kc8 247. Qd5 Kc7 248. Qd7+ Kb8 249. Qd8+ Ka7 250. Qb6+ Kb8 251. Kf7 Kc8 252. Ke8 Kb8 253. Kd7 e3 254. fxe3 Nf6+ 255. gxf6 exf6  256. e7 Qa7 257. e8=Q#

Here is the longest problem that has a promoted piece and some minor duals in the solution.
[Title "Nenad Petrovic, Zagreb 1969, Mate In 271"]
[FEN "8/Bk3p1p/1P3p2/KP2n2p/1P1p4/1Pp2p2/B1P5/7B w - - 0 1"]

1. Bb1 h4 2. Ka4 Ka8 3. Ka3 Kb7 4. Ka2 Ka8 5. Ka1 Kb7 6. Ba2 Ka8 7. Kb1 Kb7 8. Kc1 Ka8 9. Kd1 Kb710. Ke1 Ka8 11. Bb1 Kb7 12. Kf1 Ka8 13. Kf2 Kb7 14. Ke1 Ka8 15. Kd1 Kb7 16. Kc1 Ka8 17. Ba2 Kb7 18. Kb1 Ka8 19. Ka1 Kb7 20. Bb1 Ka8 21. Ka2 Kb7 22. Ka3 Ka8 23. Ka4 Kb7 24. Ka5 f5 25. Ka4 Ka8 26. Ka3 Kb7 27. Ka2 Ka8 28. Ka1 Kb7 29. Ba2 Ka8 30. Kb1 Kb7 31. Kc1 Ka8 32. Kd1 Kb7 33. Ke1 Ka8 34. Bb1 Kb7 35. Kf1 Ka8 36. Kf2 Kb7 37. Ke1 Ka8 38. Kd1 Kb7 39. Kc1 Ka8 40. Ba2 Kb7 41. Kb1 Ka8 42. Ka1 Kb7 43. Bb1 Ka8 44. Ka2 Kb7 45. Ka3 Ka8 46. Ka4 Kb7 47. Ka5 f4 48. Ka4 Ka8 49. Ka3 Kb7 50. Ka2 Ka8 51. Ka1 Kb7 52. Ba2 Ka8 53. Kb1 Kb7 54. Kc1 Ka8 55. Kd1 Kb7 56. Bb1 Ka8 57. Ke1 Kb7 58. Kf1 Ka8 59. Kf2 Kb7 60. Ke1 Ka8 61. Kd1 Kb7 62. Kc1 Ka8 63. Ba2 Kb7 64. Kb1 Ka8 65. Ka1 Kb7 66. Bb1 Ka8 67. Ka2 Kb7 68. Ka3 Ka8 69. Ka4 Kb7 70. Ka5 f6 71. Ka4 Ka8 72. Ka3 Kb7 73. Ka2 Ka8 74. Ka1 Kb7 75. Ba2 Ka8 76. Kb1 Kb7 77. Kc1 Ka8 78. Kd1 Kb7 79. Ke1 Ka8 80. Bb1 Kb7 81. Kf1 Ka8 82. Kf2 Kb7 83. Ke1 Ka8 84. Kd1 Kb7 85. Kc1 Ka8 86. Ba2 Kb7 87. Kb1 Ka8 88. Ka1 Kb7 89. Bb1 Ka8 90. Ka2 Kb7 91. Ka3 Ka8 92. Ka4 Kb7 93. Ka5 f5 94. Ka4 Ka8 95. Ka3 Kb7 96. Ka2 Ka8 97. Ka1 Kb7 98. Ba2 Ka8 99. Kb1 Kb7 100. Kc1 Ka8 101. Kd1 Kb7 102. Ke1 Ka8 103. Bb1 Kb7 104. Kf1 Ka8 105. Kf2 Kb7 106. Ke1 Ka8 107. Kd1 Kb7 108. Kc1 Ka8 109. Ba2 Kb7 110. Kb1 Ka8 111. Ka1 Kb7 112. Bb1 Ka8 113. Ka2 Kb7 114. Ka3 Ka8 115. Ka4 Kb7. 116. Ka5 h3 117. Ka4 Ka8 118. Ka3 Kb7 119. Ka2 Ka8 120. Ka1 Kb7 121. Ba2 Ka8 122. Kb1 Kb7 123. Kc1 Ka8 124. Kd1 Kb7 125. Ke1 Ka8 126. Bb1 Kb7 127. Kf1 Ka8 128. Kf2 Kb7 129. Ke1 Ka8 130. Kd1 Kb7 131. Kc1 Ka8 132. Ba2 Kb7 133. Kb1 Ka8 134. Ka1 Kb7 135. Bb1 Ka8 136. Ka2 Kb7 137. Ka3 Ka8 138. Ka4 Kb7 139. Ka5 h2 140. Ka4 Ka8 141. Ka3 Kb7 142. Ka2 Ka8 143. Ka1 Kb7 144. Ba2 Ka8 145. Kb1 Kb7 146. Kc1 Ka8 147. Kd1 Kb7 148. Ke1 Ka8 149. Bb1 Kb7 150. Kf1 Ka8 151. Kf2 Kb7 152. Ke1 Ka8 153. Kd1 Kb7 154. Kc1 Ka8 155. Ba2 Kb7 156. Kb1 Ka8 157. Ka1 Kb7 158. Bb1 Ka8 159. Ka2 Kb7 160. Ka3 Ka8 161. Ka4 Kb7 162. Ka5 h6 163. Ka4 Ka8 164. Ka3 Kb7 165. Ka2 Ka8 166. Ka1 Kb7 167. Ba2 Ka8 168. Kb1 Kb7 169. Kc1 Ka8 170. Kd1 Kb7 171. Ke1 Ka8 172. Bb1 Kb7 173. Kf1 Ka8 174. Kf2 Kb7 175. Ke1 Ka8 176. Kd1 Kb7 177. Kc1 Ka8 178. Ba2 Kb7 179. Kb1 Ka8 180. Ka1 Kb7 181. Bb1 Ka8 182. Ka2 Kb7 183. Ka3 Ka8 184. Ka4 Kb7 185. Ka5 h5 186. Ka4 Ka8 187. Ka3 Kb7 188. Ka2 Ka8 189. Ka1 Kb7 190. Ba2 Ka8 191. Kb1 Kb7 192. Kc1 Ka8 193. Kd1 Kb7 194. Ke1 Ka8 195. Bb1 Kb7 196. Kf1 Ka8 197. Kf2 Kb7 198. Ke1 Ka8 199. Kd1 Kb7 200. Kc1 Ka8 201. Ba2 Kb7 202. Kb1 Ka8 203. Ka1 Kb7 204. Bb1 Ka8 205. Ka2 Kb7 206. Ka3 Ka8 207. Ka4 Kb7 208. Ka5 h4 209. Ka4 Ka8 210. Ka3 Kb7 211. Ka2 Ka8 212. Ka1 Kb7 213. Ba2 Ka8 214. Kb1 Kb7 215. Kc1 Ka8 216. Kd1 Kb7 217. Ke1 Ka8 218. Bb1 Kb7 219. Kf1 Ka8 220. Kf2 Kb7 221. Ke1 Ka8 222. Kd1 Kb7 223. Kc1 Ka8 224. Ba2 Kb7 225. Kb1 Ka8 226. Ka1 Kb7 227. Bb1 Ka8 228. Ka2 Kb7 229. Ka3 Ka8 230. Ka4 Kb7 231. Ka5 h3 232. Ka4 Ka8 233. Ka3 Kb7 234. Ka2 Ka8 235. Ka1 Kb7 236. Ba2 Ka8 237. Kb1 Kb7 238. Kc1 Ka8 239. Kd1 Kb7 240. Ke1 Ka8 241. Bb1 Kb7 242. Kf1 Ka8 243. Kf2 Kb7 244. Ke1 Ka8 245. Kd1 Kb7 246. Kc1 Ka8 247. Ba2 Kb7 248. Kb1 Ka8 249. Ka1 Kb7 250. Bb1 Ka8 251. Ka2 Kb7 252. Ka3 Ka8 253. Ka4 Kb7 254. Ka5 Kc8 255. Ka6 Kd8 256. b7 Nd7 257. Bxf3 h1=Q 258. Bxh1 d3 259. cxd3 f3 260. Bxf3 Ke7 261. b8=Q Nxb8+ 262. Bxb8 c2 263. Bxc2 Ke6 264. b6 Kf6 265. b7 Ke6 266. d4 h2 267. Bxh2 f4 268. b8=Q Kf7 269. Bxf4  Kg7 270. Bh5 Kf6 271. Qe5#

In regards to the longest known correct checkmate in an illegal position that uses just pieces from the chess box, as Blathy repurposed the the light squared bishop onto a dark square.
Note-Althogh Blathy is known to have composed to slightly longer dualed, illegal mate in 292 moves, that problem is cooked, meaning it is incorrect and has a shorter solution although I still searching for an exact mention of where in the problem are the moves that Blathy missed in his analysis.
[Title "Otto Blathy, Weihnachtsgrüße 12/1929, Mate In 290"]
[FEN "bBrb1B2/P1n1r2p/1Kp1Pb1p/2pk1P1p/5P2/1P2pP2/1pP1P3/1R4n1 w - - 0 1"]

1. Rd1+ Bd4 2. c4+ Kd6 3. Rxg1 Bc3 4. Rd1+ Bd4 5. Ka5 Bb7 6. Ka4 Ba8 7. Ka3 Bb7 8. Ka2 Ba8 9. Kb1 Bb7 10. Kc2 Ba8 11. Kd3 Bb7 12. Re1 Ba8 13. Rf1 Bb7 14. Rd1 Ba8 15. Kc2 Bb7 16. Kb1 Ba8 17. Ka2 Bb7 18. Ka3 Ba8 19. Ka4 Bb7 20. Ka5 Ba8 21. Kb6 h4 22. Ka5 Bb7 23. Ka4 Ba8 24. Ka3 Bb7 25. Ka2 Ba8 26. Kb1 Bb7 27. Kc2 Ba8 28. Kd3 Bb7 29. Rf1 Ba8 30. Re1 Bb7 31. Rd1 Ba8 32. Kc2 Bb7 33. Kb1 Ba8 34. Ka2 Bb7 35. Ka3 Ba8 36. Ka4 Bb7 37. Ka5 Ba8 38. Kb6 h3 39. Ka5 Bb7 40. Ka4 Ba8 41. Ka3 Bb7 42. Ka2 Ba8 43. Kb1 Bb7 44. Kc2 Ba8 45. Kd3 Bb7 46. Rf1 Ba8 47. Re1 Bb7 48. Rd1 Ba8 49. Kc2 Bb7 50. Kb1 Ba8 51. Ka2 Bb7 52. Ka3 Ba8 53. Ka4 Bb7 54. Ka5 Ba8 55. Kb6 h2 56. Ka5 Bb7 57. Ka4 Ba8 58. Ka3 Bb7 59. Ka2 Ba8 60. Kb1 Bb7 61. Kc2 Ba8 62. Kd3 Bb7 63. Rf1 Ba8 64. Re1 Bb7 65. Rd1 Ba8 66. Kc2 Bb7 67. Kb1 Ba8 68. Ka2 Bb7 69. Ka3 Ba8 70. Ka4 Bb7 71. Ka5 Ba8 72. Kb6 h5 73. Ka5 Bb7 74. Ka4 Ba8 75. Ka3 Bb7 76. Ka2 Ba8 77. Kb1 Bb7 78. Kc2 Ba8 79. Kd3 Bb7 80. Rf1 Ba8 81. Re1 Bb7 82. Rd1 Ba8 83. Kc2 Bb7 84. Kb1 Ba8 85. Ka2 Bb7 86. Ka3 Ba8 87. Ka4 Bb7 88. Ka5 Ba8 89. Kb6 h4 90. Ka5 Bb7 91. Ka4 Ba8 92. Ka3 Bb7 93. Ka2 Ba8 94. Kb1 Bb7 95. Kc2 Ba8 96. Kd3 Bb7 97. Rf1 Ba8 98. Re1 Bb7 99. Rd1 Ba8 100. Kc2 Bb7 101. Kb1 Ba8 102. Ka2 Bb7 103. Ka3 Ba8 104. Ka4 Bb7 105. Ka5 Ba8 106. Kb6 h3 107. Ka5 Bb7 108. Ka4 Ba8 109. Ka3 Bb7 110. Ka2 Ba8 111. Kb1 Bb7 112. Kc2 Ba8 113. Kd3 Bb7 114. Rf1 Ba8 115. Re1 Bb7 116. Rd1 Ba8 117. Kc2 Bb7 118. Kb1 Ba8 119. Ka2 Bb7 120. Ka3 Ba8 121. Ka4 Bb7 122. Ka5 Ba8 123. Kb6 h6 124. Ka5 Bb7 125. Ka4 Ba8 126. Ka3 Bb7 127. Ka2 Ba8 128. Kb1 Bb7 129. Kc2 Ba8 130. Kd3 Bb7  131. Rf1 Ba8 132. Re1 Bb7 133. Rd1 Ba8 134. Kc2 Bb7 135. Kb1 Ba8 136. Ka2 Bb7 137. Ka3 Ba8 138. Ka4 Bb7 139. Ka5 Ba8 140. Kb6 h5 141. Ka5 Bb7 142. Ka4 Ba8 143. Ka3 Bb7 144. Ka2 Ba8 145. Kb1 Bb7 146. Kc2 Ba8 147. Kd3 Bb7 148. Rf1 Ba8 149. Re1 Bb7 150. Rd1 Ba8 151. Kc2 Bb7 152. Kb1 Ba8 153. Ka2 Bb7 154. Ka3 Ba8 155. Ka4 Bb7 156. Ka5 Ba8 157. Kb6 h4 158. Ka5 Bb7 159. Ka4 Ba8 160. Ka3 Bb7 161. Ka2 Ba8 162. Kb1 Bb7 163. Kc2 Ba8 164. Kd3 Bb7 165. Rf1 Ba8 166. Re1 Bb7 167. Rd1 Ba8 168. Kc2 Bb7 169. Kb1 Ba8 170. Ka2 Bb7 171. Ka3 Ba8 172. Ka4 Bb7 173. Ka5 Ba8 174. Kb6 h1=Q 175. Rxh1 Bg7 176. Rd1+ Bd4 177. Ka5 Bb7 178. Ka4 Ba8 179. Ka3 Bb7 180. Ka2 Ba8 181. Kb1 Bb7 182. Kc2 Ba8 183. Kd3 Bb7 184. Rf1 Ba8 185. Re1 Bb7 186. Rd1 Ba8 187. Kc2 Bb7 188. Kb1 Ba8 189. Ka2 Bb7 190. Ka3 Ba8 191. Ka4 Bb7 192. Ka5 Ba8 193. Kb6 h2 194. Ka5 Bb7 195. Ka4 Ba8 196. Ka3 Bb7 197. Ka2 Ba8 198. Kb1 Bb7 199. Kc2 Ba8 200. Kd3 Bb7 201. Rf1 Ba8 202. Re1 Bb7 203. Rd1 Ba8 204. Kc2 Bb7 205. Kb1 Ba8 206. Ka2 Bb7 207. Ka3 Ba8 208. Ka4 Bb7 209. Ka5 Ba8 210. Kb6 h3 211. Ka5 Bb7 212. Ka4 Ba8 213. Ka3 Bb7 214. Ka2 Ba8 215. Kb1 Bb7 216. Kc2 Ba8 217. Kd3 Bb7 218. Rf1 Ba8 219. Re1 Bb7 220. Rd1 Ba8 221. Kc2 Bb7 222. Kb1 Ba8 223. Ka2 Bb7 224. Ka3 Ba8 225. Ka4 Bb7 226. Ka5 Ba8 227. Kb6 h1=Q 228. Rxh1 Bg7 229. Rd1+ Bd4 230. Ka5 Bb7 231. Ka4 Ba8 232. Ka3 Bb7 233. Ka2 Ba8 234. Kb1 Bb7 235. Kc2 Ba8 236. Kd3 Bb7 237. Rf1 Ba8 238. Re1 Bb7 239. Rd1 Ba8 240. Kc2 Bb7 241. Kb1 Ba8 242. Ka2 Bb7 243. Ka3 Ba8 244. Ka4 Bb7 245. Ka5 Ba8 246. Kb6 h2 247. Ka5 Bb7 248. Ka4 Ba8 249. Ka3 Bb7 250. Ka2 Ba8 251. Kb1 Bb7 252. Kc2 Ba8 253. Kd3 Bb7 254. Rf1 Ba8 255. Re1 Bb7 256. Rd1 Ba8 257. Kc2 Bb7 258. Kb1 Ba8 259. Ka2 Bb7 260. Ka3 Ba8 261. Ka4 Bb7 262. Ka5 Ba8 263. Kb6 h1=Q 264. Rxh1 Bg7 265. Rd1+ Bd4 266. Ka5 Bb7 267. Ka4 Ba8 268. Ka3 Bb7 269. Ka2 Ba8 270. Kb1 Bb7 271. Kc2 Ba8 272. Kd3 Bb7 273. Rf1 Ba8 274. Re1 Bb7 275. Rd1 Ba8 276. Kc2 Bb7 277. Kb1 Ba8 278. Ka2 Bb7 279. Ka3 Ba8 280. Ka4 Bb7 281. Ka5 Ba8 282. Kb6 Bb7 283. Kxb7 b1=Q 284. Rxb1 Be5 285. Rd1+ Bd4 286. Rxd4+ cxd4 287. Kb6 d3 288. a8=Q Rxb8+ 289. Qxb8 dxe2 290. Qxd8#

Lastly, if you allow any amount of illegal material, with no first/last rank pawns and one king per side of course, here is a mate in 415 that is an extension of Blathy's above mate in 290.
 [FEN "bBrb1B2/P1n1r1bp/pKp1P2p/2pk1P1p/5P1p/1P2pP1p/1pP1P2p/1R5n w - - 0 1"]

1. Rd1+ Bd4 2. c4+ Kd6 3. Rxh1 Bc3 4. Rd1+ Bd4 5. Ka5 Bb7 6. Ka4 Ba8 7. Ka3 Bb7 8. Ka2 Ba8 9. Kb1 Bb7 10. Kc2 Ba8 11. Kd3 Bb7 12. Rh1 Ba8 13. Rf1 Bb7 14. Rd1 Ba8 15. Kc2 Bb7 16. Kb1 Ba8 17. Ka2 Bb7 18. Ka3 Ba8 19. Ka4 Bb7 20. Ka5 Ba8 21. Kb6 h1=Q 22. Rxh1 Bc3 23. Rd1+ Bd4 24. Ka5 Bb7 25. Ka4 Ba8 26. Ka3 Bb7 27. Ka2 Ba8 28. Kb1 Bb7 29. Kc2 Ba8 30. Kd3 Bb7 31. Rh1 Ba8 32. Rf1 Bb7 33. Rd1 Ba8 34. Kc2 Bb7 35. Kb1 Ba8 36. Ka2 Bb7 37. Ka3 Ba8 38. Ka4 Bb7 39. Ka5 Ba8 40. Kb6 h2 41. Ka5 Bb7 42. Ka4 Ba8 43. Ka3 Bb7 44. Ka2 Ba8 45. Kb1 Bb7 46. Kc2 Ba8 47. Kd3 Bb7 48. Rh1 Ba8 49. Rf1 Bb7 50. Rd1 Ba8 51. Kc2 Bb7 52. Kb1 Ba8 53. Ka2 Bb7 54. Ka3 Ba8 55. Ka4 Bb7 56. Ka5 Ba8 57. Kb6 h3 58. Ka5 Bb7 59. Ka4 Ba8 60. Ka3 Bb7 61. Ka2 Ba8 62. Kb1 Bb7 63. Kc2 Ba8 64. Kd3 Bb7 65. Rh1 Ba8 66. Rf1 Bb7 67. Rd1 Ba8 68. Kc2 Bb7 69. Kb1 Ba8 70. Ka2 Bb7 71. Ka3 Ba8 72. Ka4 Bb7 73. Ka5 Ba8 74. Kb6 h4 75. Ka5 Bb7 76. Ka4 Ba8 77. Ka3 Bb7 78. Ka2 Ba8 79. Kb1 Bb7 80. Kc2 Ba8 81. Kd3 Bb7 82. Rh1 Ba8 83. Rf1 Bb7 84. Rd1 Ba8 85. Kc2 Bb7 86. Kb1 Ba8 87. Ka2 Bb7 88. Ka3 Ba8 89. Ka4 Bb7 90. Ka5 Ba8 91. Kb6 h5 92. Ka5 Bb7 93. Ka4 Ba8 94. Ka3 Bb7 95. Ka2 Ba8 96. Kb1 Bb7 97. Kc2 Ba8 98. Kd3 Bb7 99. Rh1 Ba8 100. Rf1 Bb7 101. Rd1 Ba8 102. Kc2 Bb7 103. Kb1 Ba8 104. Ka2 Bb7 105. Ka3 Ba8 106. Ka4 Bb7 107. Ka5 Ba8 108. Kb6 h6 109. Ka5 Bb7 110. Ka4 Ba8 111. Ka3 Bb7 112. Ka2 Ba8  113. Kb1 Bb7 114. Kc2 Ba8 115. Kd3 Bb7 116. Rh1 Ba8 117. Rf1 Bb7 118. Rd1 Ba8 119. Kc2 Bb7 120. Kb1 Ba8 121. Ka2 Bb7 122. Ka3 Ba8 123. Ka4 Bb7 124. Ka5 Ba8 125. Kb6 h1=Q 126. Rxh1 Bc3 127. Rd1+ Bd4 128. Ka5 Bb7 129. Ka4 Ba8 130. Ka3 Bb7 131. Ka2 Ba8 132. Kb1 Bb7 133. Kc2 Ba8 134. Kd3 Bb7 135. Rh1 Ba8 136. Rf1 Bb7 137. Rd1 Ba8 138. Kc2 Bb7 139. Kb1 Ba8 140. Ka2 Bb7 141. Ka3 Ba8 142. Ka4 Bb7 143. Ka5 Ba8 144. Kb6 h2 145. Ka5 Bb7 146. Ka4 Ba8 147. Ka3 Bb7 148. Ka2 Ba8 149. Kb1 Bb7 150. Kc2 Ba8 151. Kd3 Bb7 152. Rh1 Ba8 153. Rf1 Bb7 154. Rd1 Ba8 155. Kc2 Bb7 156. Kb1 Ba8 157. Ka2 Bb7 158. Ka3 Ba8 159. Ka4 Bb7 160. Ka5 Ba8 161. Kb6 h3 162. Ka5 Bb7 163. Ka4 Ba8 164. Ka3 Bb7 165. Ka2 Ba8 166. Kb1 Bb7 167. Kc2 Ba8 168. Kd3 Bb7 169. Rh1 Ba8 170. Rf1 Bb7 171. Rd1 Ba8 172. Kc2 Bb7 173. Kb1 Ba8 174. Ka2 Bb7 175. Ka3 Ba8 176. Ka4 Bb7 177. Ka5 Ba8 178. Kb6 h4 179. Ka5 Bb7 180. Ka4 Ba8 181. Ka3 Bb7 182. Ka2 Ba8 183. Kb1 Bb7 184. Kc2 Ba8 185. Kd3 Bb7 186. Rh1 Ba8 187. Rf1 Bb7 188. Rd1 Ba8 189. Kc2 Bb7 190. Kb1 Ba8 191. Ka2 Bb7 192. Ka3 Ba8 193. Ka4 Bb7 194. Ka5 Ba8 195. Kb6 h5 196. Ka5 Bb7 197. Ka4 Ba8 198. Ka3 Bb7 199. Ka2 Ba8 200. Kb1 Bb7 201. Kc2 Ba8 202. Kd3 Bb7 203. Rh1 Ba8 204. Rf1 Bb7 205. Rd1 Ba8 206. Kc2 Bb7 207. Kb1 Ba8 208. Ka2 Bb7 209. Ka3 Ba8 210. Ka4 Bb7 211. Ka5 Ba8 212. Kb6 h1=Q 213. Rxh1 Bc3 214. Rd1+ Bd4 215. Ka5 Bb7 216. Ka4 Ba8 217. Ka3 Bb7 218. Ka2 Ba8 219. Kb1 Bb7 220. Kc2 Ba8 221. Kd3 Bb7 222. Rh1 Ba8 223. Rf1 Bb7 224. Rd1 Ba8 225. Kc2 Bb7 226. Kb1 Ba8 227. Ka2 Bb7 228. Ka3 Ba8 229. Ka4 Bb7 230. Ka5 Ba8 231. Kb6 h2 232. Ka5 Bb7 233. Ka4 Ba8 234. Ka3 Bb7 235. Ka2 Ba8 236. Kb1 Bb7 237. Kc2 Ba8 238. Kd3 Bb7 239. Rh1 Ba8 240. Rf1 Bb7 241. Rd1 Ba8 242. Kc2 Bb7 243. Kb1 Ba8 244. Ka2 Bb7 245. Ka3 Ba8 246. Ka4 Bb7 247. Ka5 Ba8 248. Kb6 h3 249. Ka5 Bb7 250. Ka4 Ba8 251. Ka3 Bb7 252. Ka2 Ba8 253. Kb1 Bb7 254. Kc2 Ba8 255. Kd3 Bb7 256. Rh1 Ba8 257. Rf1 Bb7 258. Rd1 Ba8 259. Kc2 Bb7 260. Kb1 Ba8 261. Ka2 Bb7 262. Ka3 Ba8 263. Ka4 Bb7 264. Ka5 Ba8 265. Kb6 h4 266. Ka5 Bb7 267. Ka4 Ba8 268. Ka3 Bb7 269. Ka2 Ba8 270. Kb1 Bb7 271. Kc2 Ba8 272. Kd3 Bb7 273. Rh1 Ba8 274. Rf1 Bb7 275. Rd1 Ba8 276. Kc2 Bb7 277. Kb1 Ba8 278. Ka2 Bb7 279. Ka3 Ba8 280. Ka4 Bb7 281. Ka5 Ba8 282. Kb6 h1=Q 283. Rxh1 Bc3 284. Rd1+ Bd4 285. Ka5 Bb7 286. Ka4 Ba8 287. Ka3 Bb7 288. Ka2 Ba8 289. Kb1 Bb7 290. Kc2 Ba8 291. Kd3 Bb7 292. Rh1 Ba8 293. Rf1 Bb7 294. Rd1 Ba8 295. Kc2 Bb7 296. Kb1 Ba8 297. Ka2 Bb7 298. Ka3 Ba8 299. Ka4 Bb7 300. Ka5 Ba8 301. Kb6 h2 302. Ka5 Bb7 303. Ka4 Ba8 304. Ka3 Bb7 305. Ka2 Ba8 306. Kb1 Bb7 307. Kc2 Ba8 308. Kd3 Bb7 309. Rh1 Ba8 310. Rf1 Bb7 311. Rd1 Ba8 312. Kc2 Bb7 313. Kb1 Ba8 314. Ka2 Bb7 315. Ka3 Ba8 316. Ka4 Bb7 317. Ka5 Ba8 318. Kb6 h3 319. Ka5 Bb7 320. Ka4 Ba8 321. Ka3 Bb7 322. Ka2 Ba8 323. Kb1 Bb7 324. Kc2 Ba8 325. Kd3 Bb7 326. Rh1 Ba8 327. Rf1 Bb7 328. Rd1 Ba8 329. Kc2 Bb7 330. Kb1 Ba8 331. Ka2 Bb7 332. Ka3 Ba8 333. Ka4 Bb7 334. Ka5 Ba8 335. Kb6 h1=Q 336. Rxh1 Bc3 337. Rd1+ Bd4 338. Ka5 Bb7 339. Ka4 Ba8 340. Ka3 Bb7 341. Ka2 Ba8 342. Kb1 Bb7 343. Kc2 Ba8 344. Kd3 Bb7 345. Rh1 Ba8 346. Rf1 Bb7 347. Rd1 Ba8 348. Kc2 Bb7 349. Kb1 Ba8 350. Ka2 Bb7 351. Ka3 Ba8 352. Ka4 Bb7 353. Ka5 Ba8 354. Kb6 h2 355. Ka5 Bb7 356. Ka4 Ba8 357. Ka3 Bb7 358. Ka2 Ba8 359. Kb1 Bb7 360. Kc2 Ba8 361. Kd3 Bb7 362. Rh1 Ba8 363. Rf1 Bb7 364. Rd1 Ba8 365. Kc2 Bb7 366. Kb1 Ba8 367. Ka2 Bb7 368. Ka3 Ba8 369. Ka4 Bb7 370. Ka5 Ba8 371. Kb6 h1=Q 372. Rxh1 Bc3 373. Rd1+ Bd4 374. Ka5 Bb7 375. Ka4 Ba8 376. Ka3 Bb7 377. Ka2 Ba8 378. Kb1 Bb7 379. Kc2 Ba8 380. Kd3 Bb7 381. Rh1 Ba8 382. Rf1 Bb7 383. Rd1 Ba8 384. Kc2 Bb7 385. Kb1 Ba8 386. Ka2 Bb7 387. Ka3 Ba8 388. Ka4 Bb7 389. Ka5 Ba8 390. Kb6 a5 391. Kxa5 Bb7 392. Ka4 Ba8 393. Ka3 Bb7 394. Ka2 Ba8 395. Kb1 Bb7 396. Kc2 Ba8 397. Kd3 Bb7 398. Rh1 Ba8 399. Rf1 Bb7 400. Rd1 Ba8 401. Kc2 Bb7 402. Kb1 Ba8 403. Ka2 Bb7 404. Ka3 Ba8 405. Ka4 Bb7 406. Ka5 Ba8 407. Kb6 Bb7 408. Kxb7 b1=Q 409. Rxb1 Be5 410. Rd1+ Bd4 411. Rxd4+ cxd4 412. Kb6 d3 413. a8=Q Rxb8+ 414. Qxb8 d2 415. Qxd8#


text:
A castling variant-how would it change the game?
In chess, castling can't be done if the king or relevant rook have moved. How would the basic strategy of the game change if the king and rook could castle after moving? Also, how would the game change if the queen castle as well?

In most cases, I'd imagine the queen wouldn't castle, as it would mean it would have a harder time getting out. The only useful case I can think of would be if you developed your bishop to e3 and "castled" queenside with your queen, putting it on c1, preparing for Bh6 to potentially trade off a fianchettoed bishop while also bringing your a1 rook to an active square.  Being able to castle with your king or rook after you moved would change chess quite substantially, and it'd be difficult to quantify all the changes, but if I had to guess, kings would stay in the center longer and rooks would move around more in the middlegame.

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text:
King+Knight vs King+Pawn checkmate
How is it possible for a King and Knight to checkmate a King and Pawn? I've composed a working position, but I am not sure if this can occur through a series of moves.

Two positions of this type as a mate in 2 puzzle are available at this link https://www.apronus.com/chess/puzzles/mate-in-2-problems/?teams=KNvKP

In the general case K+N vs K+P is of course a draw - or a win for the pawn if it can promote unhindered.
There is however a famous construction were the knight can force a mate against a king stuck in front of its own well-advanced rook pawn:
[fen "8/3N4/8/8/8/p7/k7/2K5 w - - 0 1"]

1.Nc5 Ka1 2.Kc2 Ka2 3.Nd3 Ka1 4.Nc1 a2 5.Nb3#

There are many variations on that theme, the first such position being published by in the Bonus Socius before 1300.

why can't 2. Ka2 be 2. a2? Looks to me like that has a high chance of ending in stalemate. EDIT: ah, it's Nb3 checkmate

Just for the record, the longest win in this endgame is 7 moves:
[FEN "8/8/8/8/p7/8/N7/k1K5 w - - 0 1"]

1. Nb4 a3 2. Nc2+ Ka2 3. Nd4 Ka1 4. Kc2 Ka2 5. Ne2 Ka1 6. Nc1 a2 7. Nb3#

The idea in this position (and other similar positions) is to stalemate the king in the corner; that forces a pawn move and when the pawn reaches a2, you'll need to have the knight positioned in such a way that it can immediately deliver mate.
Generally speaking, this only works (up to symmetry) if the pawn is on a3, the Black king on a1 or a2 and the White on c1 or c2 (otherwise, the king can escape) and the knight is both close enough (otherwise, Black can stalemate themselves) and has the right 'parity' - if Black to move loses, then White to move will only be able to draw. Likewise, if Black to move draws, then White to move wins. You can check a position in an online endgame tablebase like Sygyzy.

It is not possible for king+knight to force checkmate but a helpmate is possible.
Basically the pawn promotes to a bishop, the king moves to the opposite coloured square to the bishop with the bishop next to it and the opposing knight delivers checkmate with the king blocking off the two squares in front of the other king.
Like this:
[fen "KB6/8/kn6/8/8/8/8/8 w - - 0 1"]

This isn't the case - see Evargalo's answer for one example.

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text:
Bird's opening versus the Dutch Defence
I have played Bird's opening for around a year now, but I don't understand why Bird's opening isn't played as much as the Dutch, even though it is a tempo up. Why is this?

Even if you play the Dutch a tempo up, you don't have great chances of gaining an advantage (especially if your opponent is completely satisfied with just equalizing). As White you typically want to maximize your chances of getting some edge, and a better way to do this is by controlling more of the centre with 1.e4/1.d4, or perhaps developing a piece with 1.Nf3. The Bird's still a fine opening, but not very challenging.
In addition to this, Black doesn't necessarily have to play 1...d5 (even though it's the most popular move). He could go for something like 1...c5, 2...Nc6, 3...g6, 4...Bg7, 5...e6, etc, playing similar to how he would against the Closed Sicilian. If at any point White decides to push e4, then we've actually got some kind of Closed Sicilian where Black is fine. And if White doesn't push e4, it's kind of odd - after all, in the Bird/Dutch isn't one of the main goals to push e4/...e5?

I don't quite understand why the Dutch can be played, as White can play 2.Bg5, winning.

Bg5 wins against inexperienced dutch players. However, as someone who's played the dutch defense 5+ years, I invite my opponent to play any sidelines against the dutch. The propensity for my opponents to play sidelines is what actually makes the dutch good.

@CitrusCornflakes 2.Bg5 is certainly not winning.

From my experience in playing the dutch(leningrad and stonewall) and the bird(typically reverse leningrad dutch), I feel its very tough to get an edge but lets people get a levelled game. You also don't really surprise people.
Half my games goes something like this
f4 d5 Nf3 c5 g3 g6 Bg2 Bg7 O-O Nf6 d3 O-O, and from here white has several options but even in white manages to get e4 in, there doesn't seem to be a path to advantage. You don't get a surprise factor when you reach this position either, since most d4 players have experience in this type of structure against the dutch systems.
Another big portion, against the sicilian players, gets something similar to the closed sicilian.
And there are of course other legitimate options.
The only things going for it is

unfamiliar to opponents(though as mentioned above, sicilian and d4 players typically comfortable). e4 players may have some problems dealing with this however, as they can't borrow their knowledge from else where.
from's gambit is bad. Just accept it. Less recommended is to transpose to the king's gambit, but
if you know your opponent doesn't have experience in the king's gambit, you could use that to your advantage.


text:
Hanham Variation Philidor Defense
I want to find a way of transposing into the Hanham Variation of the Philidor Defense, without a way for White to deviate. For example, in the normal move order, White may have the move 3. Bc4 or 3. Nc3, which I want to avoid. I have tried the Pirc defense, but it doesn't work. Is there any other opening which will transpose?

It'd be helpful to explain what variation you're talking about in the question itself

No.  Black cannot reach the Hanham variation (e.g. the Philidor setup with Nd7, Nf6, e5 and sometimes c6) by force.
The modern move order to reach the Hanham variation, however, is 1. e4 d6! 2. d4 Nf6 3. Nc3 e5.  This is black's best move order to reach the Hanham variation because white usually transposes to the Hanham variation with 4. Nf3.
Experienced white players usually don't avoid the Hanham with the above move order because the main alternative 4. dxe5!? lets black equalize easily as recent results have proven.

However, White will get a lead in development after 4.dxe5.

Engine indication gives a large advantage to White after 4.dxe5 at 40-ply.

There’s a big gap here between the engine analysis (which has white up around a pawn) and practical results in the databases (which have black not only equal, but winning more often than losing).

Playing out a game around 25-ply, stockfish quickly ends up in an opposite colored Bishop ending with white up a pawn that looks like a dead draw to me.


text:
Latvian Gambit recommendations
The Latvian gambit:

e4 e5 2. Nf3 f5!?

leads to a sort of King's gambit reversed. I've had a large winning percentage for this opening as Black in club games. Would this opening be good for a 1500-Fide level tournament?

Yes, I believe so.
The key point here is this:

I've had a large winning percentage for this opening as Black in club
games

Play what you know best, and are most comfortable with, and at 1500 FIDE Latvian Gambit is sound enough; this is is probably true even at 2000 FIDE if not higher.
Edit:
I took a look at some statistics on Latvian Gambit at lichess.org database
Masters:

All Lichess.org users:

The results indicate that Latvian Gambit is very questionable on Masters level, but at lower levels has good practical results.

Statistics alone are not enough to determine whether an opening is sound. For example, Black outperforms White in the exchange variation of the French Defence, not because Black is better, but because it's used by weaker players against stronger ones. Also note that the effect of the "surprise factor" is exaggerated in online blitz games when compared to on-the-board

@David, Good points, I think it would be better to look at result of FIDE rated matches between players of 1400 - 1600, while keeping the relative strengths in mind, but I don't know if that data is available.

@Akavall id imagine it would be somewhat difficult, but if i had a big PGN file of FIDE rated matches, I could filter for games in the Latvian in players of that rating range using Python probably without too much effort for coding.

It might barely be playable at 1500 FIDE. However, as others pointed out, if someone prepares for you, then you will be in big trouble.
My recommendation to to avoid playing this gambit at all costs.
I'm around ~2170 USCF, and my main repertoire is non traditional(morra gambit, kings gambit, alekhine, dutch....). This is coming from someone who's played many gambits over the years.
I tried earnestly to incorporate the Latvian gambit as some sort of surprise weapon. It is just unplayable. Even when my opponents were significantly weaker than me and obviously didn't know what was going on in the opening, they usually get an edge, and it could be a big one too. If they happen to have studied the latvian, then you are pretty toast. I don't even recommend it for blitz.
This is just my anecdote, but it's clear to me that for strong chess players the latvian is not sound, and it is not hard for white to deal with.

that's very surprising. We're talking about classical time controls OTB tournaments?

Sorry, actually my friend plays the Schliemann defense (1.e4 e5 2.Nf3 Nc6 3.Bb5 f5?!), not the Latvian. I remove my previous comment and my undeserved downvote.

that's fine, it happens.

Absolutely. You can. Even if your opponent plays well and gets an edge, at the levels we are discussing that won't be decisive. But the question is "why?":
If you enjoy or feel comfortable with that particular type of position, and it will make you have a nice time playing the kind of chess that you like, then sure. Go for it!
If your choice is based on results only, then is the Latvian really the best you can do? Of course it's a nice surprise weapon and you can use it against the type of player that will have a hard time against it, but I bet the time you need to have a decent knowledge of the Latvian gambit would be better invested in something like the French (not only in the short term due to the objective advantages but also in the long term as your chess will improve)

I'm assuming you're asking if this would be good for Black to play. If so then it seems fine for a 1500ish level. However, if your opponent is specifically prepared before the game (e.g., with engines and/or a coach), then you might run into some trouble.
You could incorporate this gambit into your repertoire, but I'd recommend playing other lines too, in order to make it harder for opponents to potentially prep for you. If you alternate between 5 lines and this is one of them, it becomes that much harder for people to be ready for you.

Would King's gambit be slightly better?

@CitrusCornflakes Well, the King's gambit is equal for White while the Latvian Gambit is worse for Black. So in a sense it's better, but as White you should usually be trying for some kind of edge. If you play an opening that is relatively easy for Black to equalize in, you're not utilizing your first move privilege fully.

The objective evaluation of those variations does not matter a lot, what matters at this level is whether the openings offer you practical chances. KG offers a lot of practical chances, the Latvian gambit not so much, as it is very hard for Black to create complications.

@ B.Swan Well, it depends. If a system is objectively poor and a well known refutation or quick equalizer (if you're White or Black) exists which can be easily memorized, then someone at the 1500 level could do well against it. For practical chances, the King's Gambit can offer some, but if Black knows how to respond then it's unclear who has the easier side to play.


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Castling vertically problem
I've once saw a joke chess study about castling vertically. However, I have forgotten who has composed it. I remember that in the positions, all the pawns were locked, but not much else. Does anybody know who was the composer of this problem?

I believe this is the position with White to mate in 3:
[Title "Tim Krabbé, Schaakbulletin 1972, Mate In 3"]
[FEN "8/8/4P3/3p4/2p3p1/1pP1kPPp/1P5P/R3K2R w KQkq - 0 1"]

Max Pam found a loophole in the rules, and Tim Krabbé exploited it when he composed this problem in 1972.
There are 3 variations depending on Black's responses with the third variation being vertical castling.

1.e7 Kd3 2.e8=R gxf3 3.0-0-0#.
1.e7 Kxf3 2.e8=R d4 3.0-0#.
1.e7 Kxf3 2.e8=R Kg2 3.0-0-0-0#!.

It should perhaps be noted that it was OK  when it was composed ('streng nach FIDE' -- that is, according to the letter, though not the intent), as the then rules did not state that castling could only be done on the first and last ranks, only that the pieces involved must not have been moved. That was fixed in short order, and this is now mostly a curiosity.

The concept has been traced to a Danish composer in 1907:
[Title "Conrad Staugaard, Skakbladet 11/1907, mate in 2"]
[FEN "6B1/4P3/8/8/8/2pk4/2N5/4K2R w - - 0 1"]

It has recently been named "Staugaard castling", although the term "Pam-Krabbé castling” can still be found. There has been a resurgence of compositional interest, with as of now 44 problems in the PDB database: https://pdb.dieschwalbe.de/search.jsp?expression=K%3D%27Staugaard%27

Modern Chess is so funny and still has loopholes.

The background for this is slightly different, though: the Krabbe-Pam castling was to illustrate a shortcoming in rules of chess.  This problem competed in a chess joke tourney. (It was published in Skakbladet, v. 4, i. 5 (Nov., 1907), p. 76.)

@user30536 There’s a big overlap between jokes and illustrations of rules loopholes. Thanks very much for the publication details which I’ve added to PDB


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King's gambit line refutation
In the King's gambit, a strong opponent has played against me(as black):
1.e4 e5 2.f4 exf4 3.Bc4 h6(trying to hold onto the f-pawn).
I have found a variation where White probably has a strong initiative, but he still insists that Black is fine and is slightly better.
4.d4 g5 5.h4 Bg7 5.hxg5 hxg5 6.Rxh8 Bxh8 7.Qh5
I have stopped my analysis here, since Black has a refutation 7... Qf6. I put this position into the engine, which gives White a large advantage, but Black has an extra pawn. Where did I go wrong?

What do you mean where did you go wrong?

8...Qf6 is hardly a refutation, black's position is miserable. As you also saw with the engine.

So I'm not sure if you're asking where you went wrong analyzing this line for Black (because of the large advantage the engine gives to White) or for White (because you think Black being up a pawn is important).
If you mean analyzing for Black, 4...g5 is a poor move (3...h6 is also not great, although Black still seems alright). There are a few better moves, such as 4...d5. The point is to meet 5.Bxd5 with 5...Nf6, and 5.exd5 with 5...Bd6. Probably a more challenging try for White would have been 4.Nc3, aiming to prevent ...d5. Coming back to Black's point of view, by the time 6.hxg5 is played White already has a clear edge. But still a better response would have been 6...Nc6 or 6...d5; 6...hxg5 gives White a winning position.
If you mean analyzing for White, the only arguable improvement in your analysis is 4.Nc3 instead of 4.d4. By the final position after 8...Qf6, the engine gives White a huge advantage - the lost pawn is irrelevant. White could follow up with Nc3, Nf3, e5, etc, enjoying an overwhelming initiative. Reaching this position is a disaster for Black, and definitely not for White.


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How to play the French as White
Club opponents frequently play the French Defence again me, and I have trouble countering it with the Advance variation, since  Black gets active pieces. Is there another good variation that avoids the Winawer, while giving White less problems?

Your best bet is to play the Exchange Variation with 3. ed.
[fen ""]

1. e4 e6 2. d4 d5 3. exd5 exd5

Yes, white's advantage after this is very small but you will get a more open game which is probably not what your opponent was hoping for. It has a bit of a dull, boring reputation because one line is symmetrical but there is lots of scope for both players to play more adventurously by breaking the symmetry. The tactics just take a bit longer to build.

Would immediately playing 4.c4 be a good line?

@CitrusCornflakes: The problem with 4.c4 is that Black can play 4...Bb4+, which isn’t so great for White. It’s generally better to delay c4 until Black has already spent a tempo on that bishop (e.g., 4.Nf3 Bd6 5.c4).

Three most common replies to the French are 3.Nc3, 3.Nd2 and 3.e5, in your question you are ruling out 3.Nc3 and 3.e5, so 3.Nd2, the Tarrasch, seems like a natural suggestion, and it is less sharp than Winawer and if closing of the center happens it is on better terms for white than in Advance variation, so it might be worth a look. But if you want to avoid French structures in general, then by all means play the exchange variation that Brian Towers has suggested.


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Benoni Theory Help
I've got an important tournament game coming up, and I will be playing Black. I will play the Scandinavian if White plays 1.e4, but I won't be able to unbalance the game properly after 1.d4, except if I play the Benoni(Old Benoni cuts out all transpositions). I don't like the Czech Benoni, where the break f7-f5 weakens my kingside.
Is there a line for Black in the Benoni that is tactical, sound, and stops White from getting a large center?

Why are you not able to unbalance the game by playing another of the Indian defenses or 1...d5 variations?

"Benoni" and "stops White from getting a large centre?" Hmmm, the first phrase that comes to my mind is "mutually exclusive".

f7-f5 does not weaken your kingside

The Benoni is quite a broad church, with many sub-cults, so it might help if you give a bit more detail about what you are playing beyond 1 d4 c5 which I assume is what you mean by the Old Benoni - if so I hope you are ready to play the black side of a Sicilian!

@Annatar I wish to avoid the Queen's Gambit, and my opponent would probably have prepared for Indian defences.

The whole point of letting white get the large center while you don't have that is that it unbalances the game.

The whole point of hypermodern openings like the Benoni is to encourage a big center. If you don't get that you'd probably be better off playing something else.
The Dutch leads to unbalanced positions, avoids transpositions and can be learned very quickly. The Tarrasch also. Those sound like better choices.

Someone afraid that "f7-f5 weakens [their] kingside" might not be ready for playng the Dutch...

If you don't feel comfortable playing against large centers you shouldn't play Benoni nor other openings such as KID (which both, by the way, are good choices if you look for imbalanced positions).
I would recommend, based on the proximity of the tournament and your aim for imbalaced positions, to look at Von Hennig-Schara Gambit, which doesn't have a lot of theory and usually leads to sharp play.


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Shortest stalemate in serious tournament game
I am looking for the shortest stalemate that has occurred in a serious chess game (there were no agreements between the players). So far, I have found only compositions, but is there a real game where stalemate has happened within the first 30 moves?

Yes, there has been a stalemate in a serious game that is under 30 moves long. According to Tim Krabbe's "Chess Records," the fastest such game happened in 27 moves.
[Title "Sibilio-Mariotti, Ravenna, 1982"]
[fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1. e4 e6 2. Nf3 d5 3. e5 c5 4. b4 cxb4 5. d4 Nh6 6. a3 bxa3 7. c3 Nf5 8. Nxa3 Nc6 9. Nb5 a6 10. g4 Bd7 11. Bg5 Be7 12. gxf5 axb5 13. fxe6 fxe6 14. Rxa8 Qxa8 15. Rg1 Qa3 16. Bxb5 Bxg5 17. Rxg5 Qxc3+ 18. Kf1 O-O 19. Bxc6 Bxc6 20. Kg2 Ba4 21. Qe2 Bc2 22. Ne1 Bxe4+ 23. f3 Rxf3 24. Nxf3 Bxf3 25. Qxf3 Qd2+ 26. Kh3 Qxg5 27. Qf8+ Kxf8

Interesting.  Black has what would appear to be a winning advantage, but the queen sac allows white to avoid a loss.  Were it not for that, Black's advantages would be crushing.  Black has both a mating threat via e.g. h5 Qg4++ and a queening threat on b1.  If White had e.g. an extra pawn somewhere that could move but wasn't too well placed, black could win easily.

@supercat: Now I'm trying to figure out where White explicitly decided to start playing for a stalemate. I can't see any other logical purpose to 19. Bxc6.

@Kevin According to a computer analysis from Lichess (https://lichess.org/rl8sul4u#45), Black had a huge advantage up to move 23, but then misplayed. Black would have kept the advantage if they played something like Bf5. White made a mistake on move 14 by not capturing the b5 pawn, and then subsequently trading pieces, which left Black with a passed pawn on the queenside.

@TobyMak: Indeed, move 23 for black would look like a good move except for the possibility of stalemate, which Black probably hadn't foreseen.  After that, White's best realistic outcome is a draw, and best play by both sides would lead to stalemate.


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Finding a Seirawan game
I am looking for a game played by Seirawan. I remember in the position that Black was heading for a Botvinnik formation(c5 and e5 but without d6 yet), and White had sacrificed a knight on e5 for an attack. I am 80% sure that Seirawan was Black.

Do you mean the pawn structure with c5-d6-e5? Or are you referring to the Semi-slav variation.

Probably this one:
[FEN ""]
[Site "it"]
[Date "1993.??.??"]
[Round "7"]
[White "Granda Zuniga Julio E PER"]
[Black "Seirawan, Yasser"]
[Result "1-0"]
[BlackElo "2595"]
[ECO "A30h"]
[NIC "EO 40.6.2"]

1.Nf3 Nf6 2.c4 c5 3.Nc3 e6 4.g3 b6 5.Bg2 Bb7 6.O-O Nc6 7.e4 e5 8.d3 g6 9.Nxe5 Nxe5 10.f4 Nc6 11.e5 Ng8 12.f5 Nh6 13.Ne4 Nxf5 14.Nf6+ Ke7 15.Nd5+ Ke8 16.Nf6+ Ke7 17.g4 Nfd4 18.Qe1 Qb8 19.Nd5+ Kd8 20.Bg5+ Kc8 21.Rxf7 Ne6 22.Bf6 Ncd8 23.Re7 Rg8 24.Re8 Bc6 25.Bxd8 Nxd8 26.Nf6 Rh8 27.Bxc6 dxc6 28.Qe4 Qc7 29.e6 Bg7 30.e7 Rxe8 31.Nxe8 Bd4+ 32.Kh1 Qd7 33.Nd6+ Qxd6 34.e8=Q a5 35.Rf1 Ra7 36.Rf8 Rd7 37.Q4e6 Qxe6 38.Qxe6 Kc7 39.Qe2 Bg7 40.Rf2 Bd4 41.Rf3 Nf7 42.Rf4 Nd6 43.Kg2 Nc8 44.b3 Re7 45.Re4 Rf7 46.Qe1 Rd7 47.Qg3+ Kb7 48.Re6 Bc3 49.Qf3 Nd6 50.Qf8 Nc8 51.Re8 Rc7 52.Rd8 Bg7 53.Qe8 Bf6 54.Rxc8 1-0

Yes, this is the one.


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Bird's Defense Deferred
In the Bird's Defense Deferred in the Ruy Lopez(1.e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nd4), why can't White take the e5-pawn?

In the case of 5.Nxe5 Qe7 6.f4 b5, Black will meet both 7.c3 and 7.Bb3? with 7...d6. E.g., 7.c3 d6 8.cxd4 dxe5 is apparently around equal.
A better response for White is 5.Nxd4 exd4 6.0-0. This is an improved version (for White) of the Bird's Defense, since now ...c6 won't come with tempo. In the normal Bird's Defense with the bishop on b5, ...c6 was a key resource.

Is there any point to "deferring" Bird's defense? Is that a real opening?

@bof I google searched the name and it looks like a recognized system at least. One point could be restricting the number of squares White's bishop can retreat to (just b3, instead of c4, d3, or e2). However, this doesn't mean much and having the bishop on a4 (away from ...c6) favours White.


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Canal Attack Stockfish Indication
Apparently, Stockfish on depth 22 states that the Canal Attack is the best opening after 1.e4 c5 2.Nf3 d6. Is something wrong with Stockfish?

you mean e4 c5 Nf3 d6.

In such a main line position, trusting an engine on move 2 won't be very useful.

First of all, stockfish and other chess engines don't have the best reputation of being good at openings, often misevaluating this particular phase of the game. Second of all, Canal attackis perfectly respectable opening. After e4 c5 Nf3 d6, at depth 30, I get
0.53 d4
0.44 Nc3
0.40 Bb5+(canal)
with these three constantly changing positions at different depths. Just so happens that at depth 30, d4 was the most favored, but on 31, my engine switches to Nc3, for example. They are all perfectly reasonable moves, but its not like you can just turn on the engine and expect it give you a verdict about which of the three moves I mentioned are the best.


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Finding a Kasparov Game
I remember seeing a Kasparov game, where Black played a classical bishop sacrifice. He was playing against a computer, and I'm pretty sure it was Deep Junior. I have tried to find this game, but it doesn't seem to be anywhere.

The 2003 game Kasparov-Deep Junior ) was a draw by repetition. Deep Junior played a bishop sacrifice on h2 and then forced the draw by repetition.
[Title "Garry Kasparov-Deep Junior, FIDE Man-Machine WC, New York New York USA, 1/26/2003"]
[FEN ""]
[startply "19"]

1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 O-O 5. Bd3 d5 6. cxd5 exd5 7. Nge2 Re8 8. O-O Bd6 9. a3 c6 10. Qc2 Bxh2+ 11. Kxh2 Ng4+ 12. Kg3 Qg5 13. f4 Qh5 14. Bd2 Qh2+ 15. Kf3 Qh4 16. Bxh7+ Kh8 17. Ng3 Nh2+ 18. Kf2 Ng4+ 19. Kf3 Nh2+


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Bird's opening problems
I've played the reversed Leningrad Dutch for some time, and I have the problem that when I play Nd2, Black forks my rook and queen on f6->g4->e3. I never get to push my e-pawn before Black forks me in some cases. Is there any solution to this problem?
Here is a sample line.
[FEN ""]

1. f4 d5 2. Nf3 c5 3. g3 Nf6 4. Bg2 Nc6 5. O-O e6 6. d3 Bd6 7. Nbd2 Ng4 ( I have wasted a move on Nd2.)

Thinking from my Lennigrad Dutch experience - Nd2 is usually wrong, and you must play Qe1 before it in the few situations it is right.  Do you have a game you want to show us?

Nbd2 is wrong precisely because of 7... Ng4.  Your choices are Qe1, c3, or Nc3.

Okay. Got it now.

@AlexanderWoo My computer likes 7.e4.

Interesting pawn sacrifice @bof. It requires white to find Ne5 after dxe dxe Nxe and also figure out that's playable, which is not 100% obvious- however, it scores ludicrously well in the lichess database (71% for white!)

I don't understand why you accepted an answer recommending 1. e4 in a question about Bird's opening. Moreover, it is advisable to weight until you have received a few answers before accepting any of them. (By the way, you can change which answer you accept).

You have some options.  You could abandon 7. Nbd2 because it allows 7. ... Ng4; the standard choices in the main line are 7. Qe1, 7. c3, and 7. Nc3, much like the regular Leningrad Dutch.  If Black plays Ng4 while you still have e3 covered by the Bc1, you can simply proceed with your plan to push e2-e4, and maybe later kick the knight with h2-h3 to get an attack going on the kingside.  Just make sure to keep an eye out for tactics on the a7-g1 diagonal as long as Black has a knight on g4; Bird's Opening can get ugly for White fast if you miss seeing a tactic.  You'll still need to pay attention to e3; Black's main try in the strongest lines is to play d5-d4, possibly following up with Nd5, and eventually you'll need to be prepared to play against that.  If your opponents are still gifting you e6 setups though, that might be a ways off.
In the specific position you've shown with Black's lackluster e6 setup, you have the option of going straight for 7. e4 as @bof and @pulsar512b discussed, but that idea won't ordinarily be available if Black plays more demanding lines.
If you're dead set on making 7. Nbd2 work instead, then 7. ... Ng4 8. Nb3 doesn't look like the absolute end of the world to me, but the positions aren't pleasant and Black is calling the shots.

Yes. Do not play Nd2.
It is better to not play that variation of the reversed Dutch.
It is best to just play 1. e4 and avoid the issues with Birds.


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Traxler Counterattack
I've had a few looks at the Traxler counterattack before. It seems fine for Black, but somehow the engine (Stockfish) says that White has a +2.57 advantage after Nxf7, but not much advantage after Bxf7+. Why is this so, when this opening is accepted by masters?

This could be a viable question, but you need to specify which line / which position (and which engine would be nice as well).

I think this is answerable, so voting to reopen.

I've examined this from the white side, and I can say with absolute certainty that the Bxf7+ line is the line that you should play. The Nxf7 line is evaluated by Stockfish as winning initially, but when examined more deeply things get real murky down the line. Bxf7+ on the other hand is just a clear edge for white, even though it's not enough to claim that white is winning.

I can't find it now, but I remember reading this exchange on Chessbase. A player just played ...e6 on one move, and then ...e5 on the next, seemingly losing a tempo for no reason. It was clearly computer preparation however. An interviewer asked GM Viswanathan Anand what he thought about the moves. Anand replied that if the computer thinks it's fine, then it's fine. Instead you have to analyze the lines afterwards to see why it's fine.
In other words: these days computers are so strong that their judgement trumps human judgement, including those made by world champion-caliber players.
Now the fact is that computers don't like the Traxler, even at high depth. It was played in the TCEC S17 superfinal between Leela and Stockfish. Here's the first game, and here's the reverse. Note:

These engines are playing on super hardware and achieve speeds and depths that would take very long for ordinary machines. When Leela played her fifth move, she was at depth 22/62. When Stockfish played its fifth move, it was at depth 43/62.
Both finalists thought 5.Bxf7+ is the best move.
Both finalists evaluated the position after 5.Bxf7+ as +1.5 for White (more precisely, Stockfish gave +1.5 for White; Leela thought White had a 60% chance to win).
Comparatively, in the starting position, White has roughly a +0.5 advantage.
There is some fluctuation in engine eval, so e.g. if Stockfish thinks a move that is +0.1 pawns better than the next-best move, the next-best move might still be playable. However, +1 is a pretty large gap.

Therefore the only conclusion here is that the human masters are wrong. The Traxler is objectively dubious at best. Playing this can work against humans because humans cannot find a string of "only moves" in a row to hold a position, plus it's psychologically difficult to defend against a strong attack for a long time. That's why humans - even top-level humans- often crack under pressure. The Traxler also offers plenty of opportunities for both sides, which is great if you want to play for a win and/or you think you are better than your opponent. But if you play the Traxler as Black in correspondence chess, you are asking for trouble. Maybe 32-piece tablebases will show that your position isn't lost, but you would have to fight hard for equality.
Finally I'll add that it's misleading to say the Traxler is well-regarded by masters:

Wikipedia's article on the Two Knights includes this quote: "No grandmasters have regularly adopted the Wilkes-Barre as Black, but Alexander Beliavsky and Alexei Shirov have played it occasionally even in top competition"
Chess Openings Explorer gives by far the most common response to 4.Ng5 as 4...d5 (which is also the main line of the Two Knights).

I'd call the Traxler playable in human games, but only as an occasional weapon.

Are you claiming that computers are better at everything than we are? Apparently Watson is an abysmal Stock Exchange investor. As an aside Beliavsky drew comfortably against Karpov following Bxf7.

@PhilipRoe computers aren't better at everything, but they are better at almost everything that's chess-related. Beliavsky making a comfortable draw isn't sufficient evidence of viability - in the same way Miles beat Karpov with 1. e4 a6, and it's more likely that Karpov was caught by surprise than this is a good opening.


text:
New Chess Variant
If in chess, pieces have the option instead to not move, then how would the game change? I have looked through a few positions and I see that zugzwang doesn't work at all. What else would be changed?

Well for one there would be no stalemate.

Moves in chess are powerful. As any player or even engine will tell you, a move has material significance (Stockfish awards it a fifth of a pawn, visible when no moves have been played).
There are some mechanics of chess, like stalemates and, as you mentioned, zugzwang, but for openings and middlegames , it really wouldn't change much.
As an example, beginners often are unable to formulate a plan and thus waste moves, this is analogous to passing your turn and often results in a loss.
Endgames are another story entirely. King and pawn endgames rely on zugzwangs (a common example is where one side tries to infiltrate the other's pawn chain) and opposition will not be a thing anymore, thus drawing most games without a significant advantage. To put into perspective the severity of the damage, even King vs King and Rook will be drawn (because of no opposition).
It may also slightly increase wins in positions where one side plays for a stalemate, but in my opinion, the game would overall take a turn for the worse, as it mostly affects only the endgame and can ruin a hard fought game with a undeserved draw.

authors: ə̷̶̸͇̘̜́̍͗̂̄︣͟


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Most pins in a chess game
I've looked at a few chess games on ChessBase that have a lot of pins, and I am wondering, what is the most number of pins that has occurred in a game, and what is the game?

The most pins in a real game position that I know is 3 from an extremely famous game nicknamed "On Pins And Needles" by chessgames.com. Agadmator covered in a YouTube video a few years ago.
[Title "Geoff Chandler-Richard Kynoch, Edinburgh Club Championship, Scotland, 1981"]
[FEN ""]
[startply "53"]

1. e4 c6 2. d4 d5 3. e5 Bf5 4. Nc3 e6 5. g4 Bg6 6. Nge2 c5 7. Be3 Nc6 8. dxc5 Nxe5 9. Nd4 Rc8 10. Bb5+ Nc6 11. Qe2 Nf612. O-O-O Be7 13. h4 h5 14. f3 Nd7 15. gxh5 Rxh5 16. Rhg1 Nxd4 17. Bxd4 Qc7 18. Rxg6 fxg6 19. Qxe6 Rf5 20. Nxd5 Qd8 21. Qxg6+ Rf7 22. Re1 Kf8 23. Qh7 Ke8 24. Qg8+ Rf8 25. Qxg7 Rf7 26. Qg8+ Rf8 27. Nf6#

And that is why, ladies and gentleman, you should castle :)


text:
Does a KQQ vs KQ endgame position with perpetual check exist?
In such an endgame situation (no specific position), where White isn't pinning the Black queen on the first move, is it possible for Black to get a perpetual check if they move first?

The position given by Akavall is indeed a draw by perpetual, but it's a bit difficult to see because White has many different options at some moves. They can even choose to sacrifice the h2 queen, which effectively ends the perpetual (but it's still a draw).
A position where this is much easier to see is the following one:
[FEN "5k2/8/8/8/8/5q2/7Q/6QK w - - 0 1"]

1. Qgg2 Qd1+ 2. Qhg1 Qh5+ 3. Q2h2 Qf3+

White has two options each move, and the black queen simply moves to the opened line/diagonal. As mentioned in the comments, White could sacrifice a queen on f1 or h3, but even then Black can force a perpetual on f1 and h3 (though the easiest way to draw is then trading the last pair of queens).

Yes, it is possible. Here is an example:
[Variant "From Position"]
[FEN "5k2/1Q6/8/8/7q/8/8/6QK w - - 0 1"]

1. Qh2 Qe1+ 2. Kg2 Qe2+ 3. Kg3 Qe5+ 4. Kh3 Qh5+
5. Kg2 Qe2+


text:
Double Grob-Coca-cola Gambit?
I was using the opening explorer on Chess.com when I came upon the following line
1.g4 g5 2. f4 (Coca-cola gambit)!?
How did this opening get its name? It sounds like Coca-cola walked up to Fide and payed some money for some weird advertisement.

a4 b5 (CitrusCornflakes gambit)

FIDE has nothing to do with opening names.

Sense of Humor
There are several real but somewhat silly openings that gets its name. Sodium Attack (1. Na3), Ammonia opening (1, Nh3), Meadow Hay Gambit (1. a4 e5 2. Ra3 Bxa3), Picklepuss Defence (1. e4 h5 2. d4 Nf6).
No one will actually play these in tournaments or something, they serves no useful purpose (except maybe training), but they're funny. Similar to code golf.
Coca-cola is very likely just something that sounds humorous.

I was going to add Anderssen opening (1. a3) to the silly opening list, but I realized that won't support the second paragraph. It gots its name because it did happen.

@bof Alright then. Maybe 1. a3 a5 2. b4 is a more appropiate example.


text:
Endgame - 2 Rooks vs 2 Bishops
How does one checkmate with two rooks when playing against an opponent with two bishops? I am having difficulties with the bishops shutting down my rooks.

Possible duplicate of https://chess.stackexchange.com/questions/19882/2-rooks-vs-2-minor-pieces-in-a-pawnless-endgame


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Lisitsin Gambit Traps
I've started to play the Lisitsin Gambit (1.Nf3 f5 2.e4), and this opening works well for me. However, I have analysed my games and found I have neglected to take advantage of several traps. What are the main traps in this opening?

The hardest part about playing the Lisitsin Gambit is getting your opponents to play 1...f5. How do you manage that?

Wait for my opponent to play 1...f5!

Could you show us some of those games? There are many sacrifices on h7, but without further information it's hard to guess where you're making your mistakes

You can try for Zukertort Trap in the Lisitsin Gambit line.
After 1. Nf3 f5 2. e4
the trap-line is Ng5
then if the opponent sticks with his pawn on f5, and pushes d5, then, simply play d3, followed by exd3 and then play Bxd3, and notice that the king has serious weakness on one of its diagonals.
Now, if opponent replies with Nf6, then the best option is Nxh7. If black captures with Nxh7, then Bg6(check), Kd7 and then Qxd5 (mate).
You can also go for, Bxh7 instead of Nxh7, also its winning for you, after Nxh7, you play Qh5, Kd7; Nf7, Qe8, Qxd5 (mate) and if black captures the bishop with rook, then you take it with the Knight, then Nxh7, and Qh5, checking the queen and picking up the Knight.


text:
Borg and Grob comparison
The Grob is a white opening which starts with 1.g4.
The Borg(reversed Grob) is a black opening which goes 1.e4 g5, or 1.d4 g5.
Since White is a tempo up in the Borg, what difference will this make? And what is the significance of the difference?

1.e5 is illegal. 1.d4 d5 is the Queen's Pawn Opening not the Borg which would go 1.d4 h6 preparing 2...g5.

Just dropping in to mention the obvious: that a StarTrek and digital data graphics nerd like me sees "Borg" and "grob" and goes off in entirely different directions :-)

Well for 1.d4, White's able to win a pawn outright with 2.Bxg5. In 1.e4, the extra tempo gives White better chances to capitalize on Black's dubious move.


text:
Lisitsin gambit vs From's gambit
The Lisitsin gambit usually involves a bishop on d3 and a knight on g5. From's gambit has only a bishop on d6, but the gambit-accepting side has less development than the Lisitsin. How would this affect the play in both openings, and is the Lisitsin gambit good while the From Gambit dubious?

As a person who has experience in the Bird's and Dutch openings, I would say that both of them are somewhat bad responses to the Birds or Dutch. In the From's, generally white has the edge but its not as if black doesn't have counterplay. In the Lisitsin, usually something like 1Nf3 f5 2e4 fxe4 3Ng5 Nc6 4d3 e3 is something close to equal.
There is a version of the from's gambit that goes
1f4 e5 2fxe5 d6 3exd6 Bxd6 4Nf3 Nf6, which is similar to lisitsin as black often plays Ng4. In the "main" variation of the froms, black is playing g5 and white typical response is to play g3, d4 Qd3. In the lisitsin, however, as white is more developed, black often gives the pawn pack to neutralize the attack.
So the answer the question, The main difference between the from's gambit and the lisitsin gambit is that in the Froms gambit, white often keeps the extra pawn, parries black threats, and has an edge(though positions are often complicated with chances for both sides). In the Lisitsin gambit, white's attack is often neutralized because black gives back his extra pawn in order to not allow white to develop the light square bishop quickly. The game is close to equal.
So in both gambits, if the acceptor doesn't hasn't much knowledge in the gambit, it can be very dangerous. However, if the acceptor is an experienced dutch player or bird player, then there will be no problems and the gambiteer would have had better chances with more mainstream responses.

Chessplayers need to think of the opening more in terms of plans than in moves. Whether either the From or Lisitsin is good or bad, and any benefit from White's additional move in Lisitsin isn't as important as familiarity with this pattern:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
[Result ""]
1. g4 e5 2. f3 Qh4#

Oh, everyone knows that one. But it's at the heart of From's Gambit, because 3...Bd6 threatens mate in 3.
Relating the Fool's Mate pattern to Dutch and Bird games enables you to play many good ones. I always get a kick out of Teed-Delmar because Delmar was such a good player:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
[White "teed"]
[Black "delmar"]
[Result "1-0"]

1. d4 f5 2. Bg5 h6 3. Bh4 g5 4. Bg3 f4 5. e3 h5 { Part of the disaster stems
from Black being good enough to find a move like this. Qh5+ is cut off by the
rook, and if 6. exf4, then 6...h4 traps the bishop in a different way.}  6. Bd3
Rh7 7. Qxh5+  1-0

And this one:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

1. d4 f5 2. h3 Nf6 3. g4 fxg4 4. hxg4 Nxg4 5. Qd3 Nf6 6. Rxh7

We used to think Gibaud-Lazard was the shortest game by masters on record: 1. d4 Nf6 2. Nd2 e5 3. dxe5 Ng4 4. h3 Ne3 0-1
There are dozens or hundreds of brilliant miniatures in the From Lisitsin family. Play in that style, and you'll enjoy it tremendously.

In yourseoncd game, you mean 6...Rh6, not 6...Rh7. Although I am not convinced this is too relevant to the question...

Right, thank you. It's 6...Rh6.
I think my answer is wholly relevant to the question. Whether it's a From Gambit or a Lisitsin Gambit, the moves aren't as important as the style plus the plan of checkmating them on that Foolish diagonal.


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Benoni e4-e5 push
In the Benoni, a common move in the position is e4-e5 and then Ng1-f3. Afterwards, I have worries about my opponent playing e4-e5 and creating a passed pawn, but up to now, I haven't met with this situation yet. How can I defend against e4-e5 properly?

There's no general positional method here, though you should know that your queenside knight belongs on c7 (via a6) in many lines.  You just need to know your defensive tactics very well, and, if possible, have your queenside pawns rolling before white is ready to push the e pawn.  There were a few years in the 80s and 90s when top players thought the Benoni was broken by the Taimanov attack, and it's still considered a very tricky opening.  Also, white should have lots of trouble keeping that isolated passed pawn.

Let me quote GM Mauricio Flores Rios from "Chess Structures - A Grandmaster Guide":  "Once Black gained the initiative there was little White could do to fight back. This is often the case in the Benoni structure; the position is difficult to hold once Black’s queenside majority begins its march. " The Benoni is a dynamic, counter-attacking system. Often the best way to stop White doing what he/she wants to do is by making so much trouble that they don't have time for to do it ...

The answer is going to vary depending on what exactly you mean. The e5 push is a lot stronger in f4 lines like the Taimanov than it is in the main lines because the f pawn supports the e5 pawn.

This is the crux of the Modern Benoni, right?
Do you know why you're playing the Benoni in the first place? You're trying to post a knight on e5. That's why that square is most critical; White is trying to run over your backwardness at d6 (the reason 6. e4, 7. f4, and 8. Bb5+ is White's most successful), and Black is trying to win the square himself because it's such a great outpost.
If Black had a fully adequate remedy for this, the Benoni would be much more popular. This is the price you pay for this splendidly unbalanced position, your open e-file, your queenside pawn majority: White might crush you in the center. The best you can do is point your pieces at it; I mean when Bb5+ comes, interposing with f6-knight stands a better shot because then the g7-bishop is directly on e5.
You might try Dzindzichashvili's peculiar 1. d4 g6 2. c4 Bg7 3. Nc3 c5 4. d5 Bxc3+ 5. bxc3 f5, a weird hybrid of Benoni, Dutch, Nimzo-Indian, aimed at gaining enough control over e4 so White can't so easily achieve e2-e4-e5, etc.
Good luck. Study Tal games.

Could you add a few lines demonstrating what you have described?

"Lines" not so helpful (White's tried 15 different moves). GM Henley says Black's just probing for weaknesses. Steures-Welling, 6. Bf4 d6 7. e3 Qa5 8. Qb3 Nf6 9. Bd3 Nbd7 10. Nf3 Nb6  11. Nd2 Bd7 12. e4 kinda suspect, losing touch with c4 fxe4 13. Bxe4 Ba4 14. Qb2 Qa6 15. Rb1? Nxe4 16. Nxe4 Qxc4 0-1
Debashis-Kasimdzhanov: 6. e4 going straight after e4 was thought most practical fxe4 7. f3 d6 8. fxe4 Black happy about  e5 iNf6 9. Bd3 Bg4 10. Nf3 Nbd7 11. h3 Bxf3 12. gxf3 Nh5 poking for tactics 13. f4 e5 14. dxe6 Qh4+ 15. Kf1 Ne5 16. Qa4+ Nc6 17. Rb1 O-O 18. f5 Ng3+ 19. Kg2 Nxh1 0-1

Where did you find the Dzindzi line?

Inside Chess magazine, while Dzindzichashvili was enjoying a good run with it. If I remember right, this game got attention: https://www.chessgames.com/perl/chessgame?gid=1040459


text:
Benoni Bc1-g5 move
In the Benoni, I often have opponents play Bc1-g5 as White, after I have fianchettoed my king's bishop. I don't know how to stop it. I know that it isn't the main theory, but I haven't found a way to break the pin. How is it possible to play the position with the white bishop on g5 so that I have as few problems as possible?
The main line that my opponents play is this.
[FEN ""]

1. d4 Nf6 2. c4 c5 3. d5 e6 4. Nc3 exd5 5. cxd5 d6 6. e4 g6 7. Nf3 Bg7 8. Bg5 *

An example line please?  That pin is usually not the best use of the bishop for White.

h6 followed by g5 looks playable to me. Stockfish suggests 8. ...a6 9. a4 h6 10. Be3 Qe7 for some reason.

This move order, without e4 and Bg7, was employed by Botvinnik in the Tal-Botvinnik 1960 WCC match. If you're interested, check it out here. In his book on the match, Tal recommends going for a quick h6-g5-Nh5 maneuver to win the bishop pair before the kingside knight can be maneuvered to c4, which (in conjunction with the bishop on g3) puts uncomfortable pressure on your backwards d6 pawn. Tal also mentions that while it looks a little weird to weaken your kingside pawns so much so early on, any attack on your king is merely illusion as your pieces are well coordinated to compensate for the few light square weaknesses.
With your specific move order, however, you're going to want to insert 9...a6 before playing g5 so as to stop the following variation: 8...h6 9. Bh4 g5 10. Bg3 Nh5? 11. Bb5+! and you cannot comfortably block the check without losing your d6 pawn. Note that Bd7 "loses" to Bxd7+ Qxd7 Ne5! with a counterattack on your undefended h5 knight.
Therefore, the recommendation according to theory is:
[FEN ""]
 1. d4 Nf6 2. c4 c5 3. d5 e6 4. Nc3 exd5 5. cxd5 d6 6. e4 g6 7. Nf3 Bg7 8. Bg5 h6 9. Bh4 a6 (9... g5 10. Bg3 Nh5? 11. Bb5+! Kf8 12. e5!) 10. a4 (10. Nd2 b5!) g5 11. Bg3 Nh5 12. Nd2 Nxg3=

A slight subtlety - even though 8...h6 is the most popular, 8...a6 first is more accurate. Then, 9.a4 h6, or 9.Nd2 h6 10.Bh4 b5. For 8...h6, White can play the fairly rare 9.Bf4, when 9...g5 and 9...a6 are met with 10.Bb5+ and 10.Qa4+ respectively. This is the point of the immediate 8...a6 move; then in the case of 9.a4 h6 10.Bf4, 10...g5 works well.


text:
Grob Opening lines
I sometimes play the Grob in blitz, where most of my opponents attack my g4-pawn with 1...d5. However, some opponents play 1...e5, leaving me in a weird position. Is there any way to play against 1...e5, while also leaving chances for many tactics along the a8-h1 diagonal?

You played 1. g4 and you're not pleased with a "weird position".
Do you know why 1. g4 has any value other than comic? You're aiming to post a knight on e4, and the g4-pawn is there to knock down ...f5.
I mean, if they're playing ...e5 and not ...d5 to give you the typical c4 counterplay, you ought to be happy with that because they're not contesting the square you want for your middlegame outpost.

Conversation at my club: "I haven't prep'ed anything against the Grob"                                    "What do you need to prep against the Grob?"                       "A straight face"


text:
Worst grandmaster by rating
https://www.chess.com/forum/view/fun-with-chess/worlds-lowest-rated-grandmaster
This is a joke thread about the 'world's worst grandmaster', Panko Smoobachuk. Seeing this post, I wondered, what is the world's lowest rated grandmaster?

The new, munged* FIDE rating website still has the old "Advanced Search" option, but the page doesn't have its own URL. There you can search for GMs from all countries sorted by rating ascending and then you get that the Russian GM, Vasily B Malinin, born in 1956 is the lowest rated GM with a standard rating of 2100.
Looking at his individual calculations shows that his rating has been in steady decline since 2004 which would suggest some life-changing event happened then, perhaps a health problem, which affected his chess playing ability.
*mung = self referential acronym = Mung Until No Good
Update: There are still a number of players in the 2100's but the Spanish GM Mihai Suba is the new lowest rated GM on 1949 and still dropping. His latest tournament results (April 2023) show that win, lose or draw and despite his decline he still loves playing chess.
He is a former senior world champion as recently as 2008  and author of Dynamic Chess Strategy, which was British Chess Federation Book of the Year in 1991.


text:
Checkmate with 3 bishops vs 1 bishop
I know that you can mate with two bishops, but I do not know whether it is possible if White has 3 bishops, and Black has 1 bishop. Is there a general method? If so, is it possible for White to checkmate in all cases, where he has n+2 bishops and Black has n bishops?

trade the one bishop :P

But is it possible to force Black to trade it?

Ask EGTB :P (15chrs)

If superior side has 2 light squared bishops and a dark-squared bishop and the inferior side has a dark squared bishop, I would not be surprised if it is a draw as you cannot mate with two bishops of the same square color.

The endgame tablebases seem to consistently give the win to White if White has exactly 2 bishops of the same square color as Black's bishop, and a draw otherwise. The strategy seems to be to bring the king to action and push Black's king to the edge. Black's bishop does not seem to be able to stop the attacks, and many lines seem to just ignore it instead of trading it.

White must have two bishops of one colour and a bishop of the other to get checkmate. White can then attempt to pin Black's lone bishop, which is. easier as more pieces get on the board. Then, White can checkmate.


text:
Seeking an explanation for Nezhmetidnov’s queen sacrifice
In this game, Rashid Nezhmetidnov sacrificed his queen for a bishop. I see that White gets an outpost on d5, but I can't find anything else that justifises the sacrifice. Is there any other compensation that exists?
[Title "Rashid Gibiatovich Nezhmetdinov-Oleg L Chernikov, Chigorin Team Cup, Rostov-on-Don USSR, 1962"]
[FEN ""]
[startply "22"]

1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 g6 5. Nc3 Bg7 6. Be3 Nf6 7. Bc4 O-O 8. Bb3 Ng4 9. Qxg4 Nxd4 10. Qh4 Qa5 11. O-O Bf6 12. Qxf6 Ne2+ 13. Nxe2 exf6 14. Nc3 Re8 15. Nd5 Re6 16. Bd4 Kg7 17. Rad1 d6 18. Rd3 Bd7 19. Rf3 Bb5 20. Bc3 Qd8 21. Nxf6 Be2 22. Nxh7+ Kg8 23. Rh3 Re5 24. f4 Bxf1 25. Kxf1 Rc8 26. Bd4 b5 27. Ng5 Rc7 28. Bxf7+ Rxf7 29. Rh8+ Kxh8 30. Nxf7+ Kh7 31. Nxd8 Rxe4 32. Nc6 Rxf4+ 33. Ke2

White doesn't get only one bishop for the queen, but two pieces: a bishop and a knight.
Moreover, Black's weak king, White's domination of the center, great outposts for his pieces and lack of prospects for Black's development (especially his rooks) fully compensate the material imbalance.

And most importantly: it just works! Sometimes principles can't give a full justification for a moves. There must be concrete variations supporting it

Nezhmetdinov was a little crazy in chess terms. That's why so many people enjoy his games.
White gets two pieces for the queen, and chances on the kingside black squares. Black's d=pawn is backward on an open file, which makes d5 an ideal square for a knight.
Not the most speculative sacrifice of Nezhmetdinov's career.


text:
Polish Opening development
The main idea of this opening is to get a mass of center pawns, for less development. How can White get his pieces out before Black can develop too many pieces?

The line that you refer to is probably 1.b4 e5 2.Bb2 Bxb4 3. Bxe5 Nf6.. I recall some early opening books saying that this was a bad defence because it surrendered a center pawn. The more modern view is that Black does get a very fast development in this line which is quite dangerous. I gave up the Polish when this started to become well-known. Until then I had good results. Often I got something like a reversed Sicilian with a very useful move thrown in.
I have not kept up with recent developments but there is an article in New in Chess
yearbook 132(2019) which is where I would go to catch up.


text:
In the open Catalan, should Black hold onto their pawn?
In the open Catalan, Black can hold onto the c4-pawn with b7-b5 and a7-a6. If so, then the queenside will have to be severely weakened. I think that this approach is reasonable and playable, but many other chess players state that it isn't good. Where could my reasoning have gone wrong?

You might have to give a specific line. There are a few traps where black loses horribly after trying to hold on to this pawn with b5 and/or a6.

It's possible to keep the pawn but at the expense of seriously weakening the queenside and fall behind in development. Keeping the pawn is certainly playable but you will need to know how not to be busted in the centre.
Keeping or giving the pawn, both possible in Catalan. Whether you like it or not depend on your personal preference.


text:
Spielmann Nimzo-indian
In the Spielmann Nimzo-indian, the position after this completely reasonable line makes the position seem that Black is winning. However, the engine evaluation gives the position as equal. What sort of compensation does White have that justifies the engine's decision.
[FEN ""]

1.d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Qb3 c5 5.dxc5 Nc6 6. Nf3 Ne4 7. Bd2 Nxc5 7. Qc2

Where Black has a dynamic advantage in the form of active pieces and more development.

Black is winning? Are you sure you posted the right moves?

After 8.Qc2 in the diagrammed position White has managed to develop 4 pieces, while Black has managed to develop 3 pieces. I don't know why anyone would assume that this is indicative of an advantage for Black, let alone a winning position.

Is Black really that much (or at all?) ahead in terms of development and piece activity?
Just counting, there are three minor pieces developed on each side, plus the White queen, while Black is to move and can castle. Pretty equal.
Black's three minor pieces surely are active at the moment, but are White's much worse? I don't think so.
Most importantly though, if we look a little bit ahead, White has much more straightforward moves to improve his position. A direct a3 will more or less force Bxc3, obtaining the bishop pair for White (with one of them on an open long diagonal to boot). The Nc5 is then in danger of being chased away by b4. Black can answer ...a5 or ...f5 (supporting e4 as a new outpost), but both moves create new slight weaknesses in a pawn structure that is already slightly weakened by trading away the "good" bishop.
Black cannot do much against moves like e3, Be2, 0-0 or Td1, either. Not breathtaking, but all very solid and natural. Meanwhile, Black's main break ...d5 is not without danger (for example, if it's played too soon after the exchange on c3, White may discover an attack on the loose Nc5 by cxd5 and Bxg7, netting a pawn).
I won't claim that White in turn has a real "advantage". If Black plays well, the game will still be about equal. But I'd actually prefer to play White.


text:
Benoni setup defence
In the Benoni, there is a certain setup for White where there is a knight on g3, and a bishop on d3. White then starts a pawn storm with f4-f5, with a large attack. How am I meant to play against this setup? Do I just trade the g3-knight off?
   rnbq1rk1/pp3pbp/3p1np1/2pP4/4P3/2NB2N1/PP3PPP/R1BQK2R b KQ - 5 9

Black to move.

Please provide the variation

The main move seems to be ...a6, seeking to expand on the queenside with double edged play. If White prevents by responding a4, there is a nice way to loosen up White's kingside: ...Ng4-e5 in conjunction with ...Qh4 should give you nice control over White's pawnstorm, meanwhile you can play on the queenside, coordinating your bishop and knights on b2.

The thing about the Modern Benoni is that White is usually trying to run you over on the e- and f- files. Black adopted a very small stance in the center (d6), and White's pawn play is the price to pay.
The difference between these two plans for white:
Bb5+, f4, Nf3, with a view toward e4-e5
and the one you describe here Bd3, Ne2-g3 with a view toward f4-f5
is that the f4-f5 plan is more likely to give Black the counterplay he desires with a knight on e5. You know that's why you play the Modern Benoni in the first place, yeah?
Go about your queenside business, and take their best shots on the f-file. If they crash through because you overlooked a tactic, you lose. If you hold them off and then jump all over the a1-h8 diagonal with your pieces, your Benoni is a success.
In other words, you're fretting over the plan for White that you should prefer to face as Black.

In this position, White king is still in the center.
I would go for Re8 (with ideas of Nxe4 followed by f5 in-case he has not yet castled; this in itself is a moral victory for Black, since White's center has been dismantled now)
If White castles immediately, then Nbd7 to add additional defense to e5 square and then look to expand on the queen side.
Also, always be on the look out for tactics in the Benoni (especially b5! or c4! or Nxe4!) I play this often and gives great winning chances even if I go a pawn down.


text:
Is Anderssen's opening playable?
There is a certain opening called the Anderssen's opening that plays like this.
[FEN ""]

a3 e5 2. h3 d5.

Black has developed two pawns, occupied the center, and opened up the lines for pieces, while White has only created weaknesses. Why, then, is this opening is said to be playabe?

Anderssen's opening is 1.a3 and is certainly playable. The first time I made a plus score in a tournament, I did it by opening all my White games with 1.a3 (only we called it P-QR3 back then). At a somewhat higher level, I believe Anderssen used it successfully against Morphy. But your continuation with 2.h3 seems a bit extravagant. After 1...e5 White normally plays 2.c4 or 2.e4. Even in your line Black has only a small advantage such as White would have in a normal opening.

who says its playable though. You can't play for an advantage opening with 1a3 2h3. You'll definitely be much worse out of the opening.

@CognisMantis, the goal of  this opening is not to play for an advantage, but for shock value.

@CitrusCornflakes. Not very much shock value. Everyone who played Basman knew that he would open like this.

This is a very solid opening, and don't really have much shock value. Really, 1. a3 e5 2. b4 is one of my favorites.

@Philip Roe  Then people who played Basman would be shocked if he played 1.e4. Ironic.

That specific opening is called the Anderssen Opening: Creepy Crawly Formation, Classical Defense
From about 1,000 test engine games it seems that its a remarkably even set up;
White : 45.5%
Black : 45.5%
Draw  : 9%
Based off that result I would say its very much playable. This is be cause you white usually plays the left side of the board slowly working towards the center;
One Notabale Game describing that concept Michael J Basman vs Yuri Yakovich - Hastings (1994)
 rnbqkbnr/pppppppp/8/8/8/7P/PPPPPPP1/RNBQKBNR w KQkq - 0 1

 1. h3 e5 2. a3 d5 3. c4 c6 4. e3 Nf6 5. b4 Bd6 6. Bb2 O-O 7. Nf3 Qe7 8. Qc2 Nbd7 9. cxd5 cxd5 10. Nc3 a6 11. Na4 d4 12. Rc1 b5 13. Nc5 Bxc5 14. bxc5 Bb7 15. c6 Rac8 16. c7 Nd5 17. Qf5 Rxc7 18. Rxc7 Nxc7 19. Be2 dxe3 20. dxe3 f6 21. O-O Nc5 22. Rd1 Rd8 23. Bc3 Rxd1+ 24. Bxd1 Qd7 25. Qb1 Be4 26. Qc1 N7e6 27. Nd2 Bg6 28. Bg4 h5 29. Be2 Qd5 30. Bb4 Kh7 31. Nf3 Nd3 32. Qc8 Nxb4 33. axb4 Qa2 34. Bf1 Bf7 35. Bd3+ g6 36. Qd7 Kg7 37. Be4 Nf8 38. Qb7 Qc4 39. Bc6 Kg8 40. Qxa6 e4 41. Nd4 Qxb4

Src: https://www.chess.com/games/view/657313

The White player in that game was Basman, not Masman. Basman has always been fond of weird openings.

interesting that there are so little draws?

The statistics are pretty much irrelevant if they don't come with average rating of players

Bit hard to evaluate the statistics of the players as they were engine games I literally scripted to play out 1000 games with the above opening ,

Any opening is playable as long as you buy into the idea that your only goal in the opening is to reach a playable middlegame, one with rough equality in center control, development, and king safety. Heeding the general opening principles while being alert to tactics will get you to a playable middlegame.
This isn't what chess book publishers and authors want you to think, they want you to think that following their advice will help you win chess games, which is a bunch of hooey.

a3 won't kill you. Neither will 1. h4 e5 2. h5, from which I won a theme tournament. But if you neglect the center and development for too long, then you get into trouble.

+1. 1. f3 does kill you, however, for weakening yourself.

g4 is probably worse.


text:
Lc0 vs. Stockfish
Stockfish analyses many positions per second and chooses the best line. Lc0 is a neural network that immediately ignores moves which don't work, but is slower. However, somehow Stockfish is better. How come that is true, when most of the positions it looks through are actually useless?

This is due to the way Neural Networks AI works;
Neural networks can only make decisions based off prior experience where as StockFish is more or less "Brute Forces" and prunes until the maximum numerical value is gained.
Theoretically if you could feed an AI like Lc0 enough game data (potentially the Chess Base Big Database) , especially with additional data like stockfish position evaluations you could create quite a powerful neural network with the ability to self move etc;
I think Lc0 could have the potential to develop new ideas; however it would require a secondary database of evaluations and scoring to determine it.

What do you mean by "with the ability to self move"?

Because Stockfish searches a LOT more positions.
Just check the latest TCEC superfinal between the two. In a typical position Leela might search 40k positions per second. Comparatively, Stockfish searches ~200 million positions per second. That's about 5000 times more positions per second. It means that Stockfish can afford to be wrong 4999 times as long as it searches the moves that are right. (This is of course simplified since it assumes there is a "right" move.)
Also worth pointing out is that it is by no means obvious that selectively searching the "best" moves is a better approach than simply searching tons and tons of them. Remember several decades ago when computer chess was new, there were two ways to approach search. The first was to get computers to "think" like humans and consider only the best candidate moves. The other, and the one that eventually came to dominate, is to search as many moves as possible. You can see similar tensions in the real world: humans only have a few babies, but some species (such as ferns) have lots of children, most of which die, but those that survive propagate the species successfully.
Finally, one should note that Leela's neural network is not always right. See this Leela blunder vs. GM Andrew Tang, along with an explanation of why Leela blundered.

But how come Leela blundered such a simple tactic? Looking at the chess clocks, we can see that Leela spent less than 0.1 seconds thinking before making the move. Under such time constraints, Leela is not really able to consider and evaluate many different moves, but instead relies heavily on her "instincts". Looking under the hood after the match, we could see that Leela thinks Qxd4 is the correct move 90% of the time in the critical position. Furthermore, Leela thinks Bh7+ is the correct reply only 10% of the time. If she had more time to double check her assumptions, she would not have blundered, but she didn't - so she did. In our estimation, Leela would have avoided the blunder if she had spent 0.25 seconds thinking before making a a move.

As this paragraph shows, Leela's instincts are not always right. Leela compensates for this by searching the other moves anyway, it just searches them less. If Leela really did ignore "moves that don't work", it would be decisively lose repeatedly.

I'll expand on a few things that Allure already mentioned:
From the question: "Stockfish analyses many positions per second and chooses the best line. Lc0 is a neural network that immediately ignores moves which don't work, but is slower."
This is not really true. Leela and Stockfish are more similar than some people seem to assume: Both will eventually look at all moves. However both spend varying amounts of time on different moves, i.e., they will spend more time on moves they think are good. The difference between the two is: Stockfish uses "humanly chosen" heuristics (of course those are also tuned, but they are still based on human ideas) to determine which move to search how much, while Leela uses a neural network to determine which move to search how much. Both engines then search that move and based on the results (that is, the evaluation) decide how much to search that move moving forward. (obviously, the better a move the more it will be searched)
The other difference is the search backup, Stockfish uses a minimax based backup, meaning it's evaluation of a line is exactly the evaluation of the final position of that assumed best variation. Meanwhile Leela uses an averaging based backup, meaning also evaluations from positions that are not part of the best line can influence the evaluation. This latter algorithm is not really possible with Stockfish since it requires storing the entire search tree, which given Stockfish's speed isn't possible. However due to the lower nodes per second of Leela because of the NN, it is possible there. Which of the two is preferable is debatable, Leela's search algorithm does have some issues.
Of course new versions of Stockfish now also use a NN, albeit one with a very different structure. That doesn't really change the answer at all though.

The simple (oversimple) answer is that Stockfish considers all moves whereas Lc0 only considers moves/positions it has in its database/neural network. In a sense Lc0 can't find new ideas whereas Stockfish can.


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Endgame theory question
Let us look at an endgame where White has 8 pawns, and Black has the e/d-pawn missing. How can White win this endgame if both sides play perfectly? I am having a little trouble.

Are you meaning a pure King and Pawn ending? If so then either side could win or the game could be a draw. It all depends on the precise pawn structure.

Just move your pawns and your kings up solidly, avoid giving counterplay. At some point you will get the opportunity to get a passed pawn, that you can then usually trade to get several pawns on a wing.
Two short game examples played against stockfish with just king and pawns in initial position while removing black d pawn. First one is very simple without any counterplay, second one is more creative with tactics.

d4 a5 2. Kd2 Kd7 3. Kd3 h5 4. e4 Kc6 5.c4 f6 6. b3 g5 7. a3 e6 8. b4 axb4 9. axb4 Kd7 10. c5 Kc6 11. Kc4 Kd7 12. b5 g4 13. d5 exd5+ 14. exd5 Kd8 15. Kd4 b6 16. d6 bxc5+ 17. Kxc5 cxd6+ 18. Kxd6 f5 19. Ke5 h4 20. Kxf5 h3 21. g3 Kc7 22. Kxg4 Kb6  etc..
Just created a majority on the Q side and eventually a passed pawn, while leaving three vs three on the king side. Only possible counterplay for black would have been to bring the three kingside black pawns to f4,g4,h4 with allows them to force the creation of a passed pawn. But it's easy to keep an eye on that resource and prevent it if it might become a threat.

e4 a5 2. Ke2 Kd7 3. Ke3 g5 4. d4 f6 5. f4 b5 6. h4 gxh4 7. Kf3 h5 8. c3 Kd6 9. f5 c5 10. b3 b4 11. cxb4 axb4 12. Ke3 e6 13. e5+ fxe5 14. dxc5+ Ke7 15. Ke4 h3 16. gxh3 Kf6 17. c6 exf5+ 18. Kd5 Ke7 19. Kxe5 h4 20. Kxf5 Kd6 21. Kg4 Kxc6 22. Kxh4 Kd7 23. Kg5 Ke7 24. Kf5 Kd6 25. h4 Ke7 26. Ke5 Kf7 27. Kd5 Ke7 28. Kc5 etc..

Gave the h pawn weakening black structure and staying with a majority on the a-f columns while black stays with 2 h pawns vs white g pawn on the king side. Eventually ended up the same way as first game, creating a passed pawn and grabbing black pawns thanks to it, after the tactics arising after 13.e5+. But 6.h4 was kinda just for fun and to show that being a pawn up allows a lot of things. 6.g4 would have been simpler, like in the first game.

A more practical form of your question relates to the Exchange Lopez and Tartakover Caro-Kann.
Euwe did a complete analysis of how White wins the Exchange Lopez pawn ending if you set up the pawn structure with no pieces on the board:
4k3/1pp2ppp/p1p5/8/4P3/8/PPP2PPP/4K3 w - - 0 1

While the Tartakover Caro=Kann is the same thing on the other wing.
In this impractical 8-vs.-7 thing you envision, the side with the extra pawn would surely begin with the unopposed pawn two squares, as the first step toward creating a passed pawn.


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Reversed openings
Reversed openings, as in ones for Black that are played by White, have a characteristic that usually main lines for Black are obscure in White, and vice versa. How would this be true, since White is only one tempo up?

One tempo is quite a big deal in most openings...

Related: https://chess.stackexchange.com/q/22407/14079

When Black plays a first move, it's usually directly related to White's first move.
1.d4 means White can't play d2-d3, so e4 is more up for grabs, which makes 1...f5 palatable. If White plays Bird's 1. f4, then From's 1...e5 2. fxe5 d6 is promising. White doesn't have that type of reply against the Dutch.
Take the Budapest. 1. d4 Nf6 2. c4 e5, and if 3. dxe5, Black typically goes 3...Ng4 with a long-term view of keeping a knight posted on e5. But if you try that in reverse with Tennison's Gambit, 1. Nf3 d5 2. e4 dxe4 3. Ng5, there's a little less to like about it. In the Budapest given, a knight on e5 has the c4-pawn to target, while that same knight for White in Tennison's gambit isn't as fortunate.
For a long time, we looked at the English Opening like this: If 1. c4 e5 2. Nc3 Nf6 3. g3 d5 4. cxd5 Nxd5, and so on, in a Dragon-Sicilian-in-reverse
way, it turns out that the extra tempo White has is usually spent wondering what to do with the queen bishop. Bc1-d2 was hardly a great use of that 'extra' move. I think the view on this has changed over the years, but you see what I mean.

Just to clarify against the Dutch 1 d4 f5 2 e4 is the perfectly respectable Staunton Gambit (https://en.wikipedia.org/wiki/Staunton_Gambit), but as white can no longer play d3 he/she can not continue along lines similar to a "reversed" From's Gambit

Absolutely. 1. d4 f5 2. e4 is White's best, said Capablanca in the 1913 Havana tournament book.

unfortunately, Capablanca is wrong.

"Capablanca is wrong". I love the Internet.


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Grunfeld Defense as White
This opening gives White a big center and aims to destroy it. I have trouble playing the exchange variation as White because Black has great piece activity while my pieces are stuck in passive positions. Is there another variation which also allows White to get a big center while minimising problems?

Have a look at the Russian System:  4.Nf3 Bg7 5.Qb3. You still get the d4-e4 center, but your queen is in the middle of the board now. Also I would recommend you to look at 5. Bd2 in the Exchange Variation, it throws many players off and you avoid the typical Exchange structure. But you will be asked question in every variation of the Grunfeld, that is what makes the opening sound in the first place. You get the center and have to care for it, Black gets to make problems.

I had the same issue too because c5, Bg7 and knights: a lot of pressure on d4 pawn. I was looking for something solid and relieving the pressure on d4. I tried Makogonov Variation 4.Nf3 Bg7 5.e3 0-0 6.b4. I can say it worked for me, at least I got some decent wins and not losing easily, I liked the logic of playing b4, I think it slows down the pressure by c5. I am an amateur (sub 2000 ELO). In this variation you may want to put your queen on b3, bishop on b2 or a3, the white colored bishop to e2 or c4... I think you have a good space and it may be out of comfort zone of black.

Any issue with playing a 2.Nf3 order when trying to fit into the rest of your repertoire?

I think Bronstein had the right idea in the Exchange Grunfeld against Boleslavsky in the 1st game of the 1950 candidates final. It costs a little material, but it's White who got the active pieces, while the center expanded.
[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
[Event "Bronstein - Boleslavsky Candidates Playoff"]
[Site "Moscow URS"]
[Date "1950.07.31"]
[EventDate "1950.07.31"]
[Round "1"]
[Result "1-0"]
[White "David Bronstein"]
[Black "Isaac Boleslavsky"]
[ECO "D87"]
[WhiteElo "?"]
[BlackElo "?"]
[PlyCount "63"]

1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. cxd5 Nxd5 5. e4 Nxc3 6. bxc3
c5 7. Bc4 Bg7 8. Ne2 O-O 9. O-O cxd4 10. cxd4 Nc6 11. Be3 Bg4
12. f3 Na5 13. Bd3 Be6 14. d5 Bxa1 15. Qxa1 f6 16. Bh6 Qb6+
17. Kh1 Rfd8 18. Rb1 Qc5 19. Bd2 b6 20. Bb4 Qc7 21. Rc1 Qb7
22. Qb1 Rab8 23. dxe6 Nc6 24. Bc3 Ne5 25. Bb5 Rbc8 26. Bxe5
Rxc1+ 27. Qxc1 fxe5 28. Bd7 Qa6 29. Ng3 Qxa2 30. h4 Rf8
31. Qg5 Rf6 32. Qxf6 1-0

Nice exchange sac. I think I might have seen something like this before.

It ought to be a familiar idea to players who want to play the Exchange, yeah?
When Purdy wrote about "the myth of the pawn center", he cited the Exchange Grunfeld as the best example of pawn centers that lack potential. I think this exchange sacrifice energizes 4. cxd5.