text:
Why does a knight combine better with the queen than a bishop does?
From this question, the couple queen + knight is strong in attacking the opponent's king.
I searched why the knight combines better than the bishop with a queen, and all I could find, from this article, is:

"Knights cooperate better than bishops with the queen, as the two
  pieces complement each other and will control the position better."

Can you explain why?

Because they aren't stuck on a single colour.

It is a fairly short and simple explanation:
They can combine to attack any square, not just squares on one color. As part of that they can also shift the attack better from one square to another.

This is also true of Q+B. So how does this make Q+N better?

@RosieF That is not true. If you have a dark-squared bishop and a queen, you can only attack g7 with two pieces, for example. You can never attack h7 with two pieces. If you reposition the knight, you can. It is that you can attack every square on the board with two pieces, obviously, after some maneuvering.

Ah -- did you mean they can both attack any square? Sorry, I misunderstood your words "to attack any square" and didn't see that you meant both pieces.

One of the ways I teach kids how knights move is to put the queen and the knight on the same square. The knight can go to the nearest squares that the queen can't go to.
It is this unique complimentary nature of the two pieces which means that they form such a potent combination. With queen plus any other piece this is missing and there is a duplication of function.
As an aside, something similar applies to the two bishops, although they obviously are always on different coloured squares. This explains why two bishops are generally worth more than 2 x one bishop.

well, except that in an actual game, they'll never be on the same square so it's not immediately obvious how that applies :)

@ilkkachu it also means that the knight can defend the queen without obstructing her movement.

@JAD, that, while it's just the reverse of the above, seems to make for a much better point.

Well, it works both ways. Knight can protect queen without getting in its way. This is important when you make some close-range attacks on king. For attacking the opponent's king, the other direction is not so important except for some positions involving a good number of pawns.

John Watson's "Secrets of Modern Chess Strategy" contains a section titled "Folklore or Reality? Queens and Knights" John lists some folks that say Queen and Knight are better

Capablanca
Shirov
Silman

And refers to Steve Meyer's book "Bishop vs Knights" which also says the Queen + Knight is better.
I am currently playing through "Karpov move by move" which has

..it is well established that queen and knight can create threats more efficiently than queen and bishop

John makes a few points.  I will simplify his points here.

examples of the superiority of queen + knight over queen + bishop are usually examples of a better knight and a bad bishop.
Statistical analysis shows a very slight superiority of the queen + knight which can be explained by the stronger side choosing queen + knight in the belief that queen + knight is superior.  that is, the queen + knight side was already winning.

John concludes

...the idea of the advantage of queen and knight over queen and bishop seems to be one of those folkloric bits of wisdom/mythology of at most extremely limited validity, and quite possibly none whatsoever.

I cannot do justice to John's analysis in this post.  If you like statistical analysis and questioning of accepted wisdom I recommend this book.  I especially enjoyed the section on the two bishops.

I have seen Watson's opinion on this before, but as the old saying says: "there are lies, damned lies, and statistics". I have seen more World Champions (the most recent was Karpov in "The Karpov Method" videos), who believe that the Q+N is superior to the Q+B, so I will take their opinion over Watson, who I like a lot. Their judgment is far superior.

It happens sometimes that human judgement fails to reach a truth that can be supplied by statistics/logic.  The supremacy of chess computers hints that this may be true in chess.  But chess is not a game of pure reason when people play it.  My own experience is that Queen + Knight is superior.  I can feel that is true.  If I am making a practical decision in a actual game, or evaluating a position or gauging the strength of a speculative attack what will most likely lead to the best practical result?  Thinking about statistics or going with how I feel?  I'll take the Queen + Knight.

but even with Watson's opinion,  there seems to be a lot of his opinion in there still, the stats aside. For example, his opinion about whether positions are already better. Maybe they are, maybe not, and even if they are, it does not prove that it still did not make that much more difference. The difference could also be simply practical: The positions are just harder to defend for humans. Again,  I will still stick with the world champions' opinions.

Sometimes, “well established” means someone respected made a guess and hundreds of people repeated it as fact.

Before 1900, the champions said that the knights were better than the bishops.  Before AlphaZero, lots of things were assumed to be correct.
In every game that I played against masters, I've always won when I had a knight versus their bishop.  My experience goes against today's general principles.

A knight and queen complement each other because they each do what the other can't. The queen can move like a rook and bishop combined, but it can't move in L-shapes and jump over other pieces. The logic here is that a bishop or rook can't help the queen so much since a queen can already move like them, but the knight has something the queen doesn't.
However, it's a big generalization to say a knight is always better than a queen for working with a bishop. In close quarters combat (say when being close to the enemy king), a knight is indeed better with the queen. But in an open game in general, a bishop can be better simply by being worth slightly more than a knight in general. The point is that Queen + Knight can be better when trying to accomplish a short-term attacking goal, where range isn't an issue.

I agree. The queen-bishop spear stabbing into the h7 pawn with a ruinous check comes to mind.

@StianYttervik Exactly, a queen and bishop can form a battery to attack from a distance.

I feel that many people before me have already answered the question, but I just want to add another dimension to the entire scenario. If you had to choose pieces which would be the trickiest and most difficult to calculate variations for it would probably by the queen and the knight. This isn't an objective answer, but it is just a point to take into consideration.

Steve Meyer, in his book Bishop v Knight, concludes the final chapter of the book, "Capablanca's Theorem – ♕+♘ is better than ♕+♗ in the Ending", as follows:

Verdict: Capablanca's intuitive insight into the advantage of queen and knight vs queen and bishop in the ending is correct. While general positional methods of evaluation are still important, the attacking force of the queen and knight can be very fierce, particularly in blocked positions or those featuring fewer pawns.

But John Watson, in his book "Secrets of Modern Chess Strategy", chapter "Minor-Piece Issues" claims that the examples are one-sided. He continues:

My own view, just from looking at a lot of examples, is as follows:
  a) an unusually large proportion of ♕+♘ vs ♕+♗ games are drawn;
  b) most games which are won by either side, as in the examples mentioned above, are characterized by that side having one or more rather obvious other advantages

Finally, and this might make the theorem a kind of self-fulfilling prophecy, he notes:

One proviso I have already noted above is that the side with the queen and knight (in the pure ♕+♘ vs ♕+♗ case) tended to be a bit stronger, for whatever reason. That alone might account for the small statistical edge for the ♕+♘. Moreover, as explained in the Introduction to this book, a perception of the superiority of queen and knight may well lead players who are in already advantageous but complex positions to convert them into what they view as a safer ♕+♘ vs ♕+♗ advantage. This would skew the percentages in favour of the ♕+♘.

The problem for the knight in the endgame is that it cannot protect a pawn that is protecting it, like the bishop can. So while Knight + Queen is better than Bishop + Queen, often the fact that a number of pawns will be present can tip the balance back to the bishop. This is especially true if the player with the bishop forces an exchange of queens.

One thing Q + B can do that Q + N cannot is to threaten remote squares. They can also, among other things, completely control two adjacent diagonals, which is a lot of territory. I vote Q + B.

Good point. If Q & B are on opposite colours, they have the power of the 2 bishops, which are widely regarded as more powerful than B & N. As you say, they can command 2 adjacent diagonals. If Q & B are on the same colour, they can defend each other, which Q & N can't. Defended by a B on a line, the Q can move along that line, still defended; this is possible with Q & N but only to a limited extent.

One way to look at it is this:

If you add bishops to a queen, you are adding to an ability that she already possesses, which is attacking on diagonals (which is a 45 deg attack).
Bishops practice their abilities each over its own color.
Bishops cannot protect one another directly.
If one bishop is captured, then the "union" of the bishops and queen is damaged greatly, since now the minor piece can only assist on one color.
If you add knights to a queen, you are adding an ability that she does not possess, the L attack (which is attacking at about 60 or 30 deg).
Knights practice their abilities on both colors, attacking one color at a time.
Knights can protect one another.
If one knight is captured, the minor piece can still assist on both colors.

Knights are harder to defend by pawns. In the rare events that you are attacking an open K, Q+B is equally lethal as Q+N. However two connected pawns can hold Q+B for a few turns or until new attackers come while Q+N has a higher chance to penetrate on their own.

Here are some stats from the Syzygy tablebase, of win and loss percentages of various material balances. This tablebase is of positions of up to 7 units, so where White has KQB or KQN, Black can't have more than 4 units.
First, let's pit the balances KQB and KQN against each other. Here, in KQB v KQN, KQB wins 25.0% & loses 21.0% of positions.
Next, for various choices of Black's balance, I tabulated White's win and loss percentages when White has KQB and KQN respectively.
By x+y% I mean x% if we presume that game ends in a draw as soon as a 50-move draw claim would be upheld, plus an additional y% if 50-move draws didn't exist.
Where each side has a bishop, Syzygy's stats relate to the whole tablebase of positions with the stated material regardless of whether the bishops are on opposite or the same coloured squares.
      | Win percentages     | Loss percentages    |
Black | KQB win  | KQN win  | KQB loss | KQN loss |
------+----------+----------+----------+----------+
KQR   | 20.3%    | 18.0%    | 47.3%    | 51.4%    |
KQPP  | 24.2%    | 20.9%    | 31.9%    | 36.3%    |
KRR   | 62.8+0.1 | 48.0+3.9 | 19.5%    | 23.0%    |
KRBB  | 52.4+4.2 | 52.5+0.8 | 22.8%    | 25.6+0.8 |
KRBN  | 58.1%    | 55.1+6.5 | 21.4%    | 23.2%    |
KRNN  | 58.9%    | 53.7%    | 18.7%    | 20.1%    |
KRBP  | 68.1%    | 65.6%    | 20.8%    | 23.2%    |
KRNP  | 70.9%    | 68.7%    | 19.2%    | 21.3%    |
KRPP  | 74.4%    | 72.0%    | 17.9%    | 20.0%    |

So, against the black material balances shown, KQN loses more than KQB loses. KQB wins more than KQN wins, with few exceptions.

The bishop is in general, a weak end game piece.
In some end games the bishop is more valuable than a knight, but this is only if the bishop is your only piece that can move an arbitrary distance in a single move. That's an important end game function for being able to snatch pawns while still providing pressure from a distance.
As long as this "spooky action at a distance" function is covered by some other piece, the knight is generally stronger, which is why it pairs better with a queen.

Confused about the downvotes

I believe the bishop is generally considered to gain strength relative to the knight as the game progresses, because the emptying board gives it more mobility.

@hkBst It's true, it gains mobility. But the value it gets from the mobility is greatly decreased when you have another piece that is already mobile

That is like saying two queens is only slightly more powerful than one queen, because the mobility of the second is already included in the first.

@hkBst No it isn't. Not at all. The queen is universally the strongest piece in almost every single situation. The second queen is of course less valuable than the first one however. But to say "only slightly more powerful" is a complete misrepresentation of what I'm saying at all. Or you just completely don't understand the argument.

Don't understand the downvotes, even though I don't agree with the answer. I certainly don't understand how a second queen is less valuable that the first. They have exactly the same value.


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What level of player is Kasparov's MasterClass suited for?
I am about 1400. I was wondering if I should pay for Kasparov's MasterClass, but I am not sure if it is worth the money.
Has anyone bought this?

I have seen the materials in the program, and they are for players well below your level of play. I am not sure that they are even for a 1000 player since they are very basic. While he uses positions, they are more about teaching basic terminology and showing various themes, but on a very basic level.
For example, here is one position that you are to find 5 different skewers (Bf3, Bb3, Qg2, Qh1, and Rh5).
 [FEN "6n1/1r6/8/q2k4/8/7R/7Q/3B1K2 w - - 0 1"]

The most “difficult” problems are really no more than two- or three-move tactics like this one.
 [FEN "5rk1/p3P2p/1p4pb/q7/3N4/1P4Pb/PB3Q1P/6KR b - - 0 1"]

 1... Qe1+ 2. Qxe1 Be3+ 3. Qxe3 Rf1#

The vast majority of these problems are very famous, and can be found in other books. He does give book recommendations, but they are ones that have been recommended here many times already, including by myself. He has some practical advice about how to study, but again, it is mostly common sense that may have seen recommended already right here on SEC.
Of course, Kasparov is great, and if you were much weaker, I would have a different opinion, but my verdict is that you probably would be wasting your money.

P.S. I run the high school chess club in my town, and one of the kids is rated 1256 USCF, and from having played him many times, I do not think he would find the material challenging.

YouTube keeps popping up a promo for this to try to get me to buy it...  But from what I see of the course material from the promo, it appears to me to be aimed at people who are new to chess.

@patbarron Again, I have been playing for 40 years, and I have seen many players from new to GM in that time, and I have to agree totally: It is aimed a very wide audience that is more than "I just play chess", meaning, they are truly interested, but certainly well below someone, who is already a learned beginner.

@PhishMaster  kids are always underrated by USCF as they progress faster than the ratings can catch up.

And tha only makes this course worse for kids, but the OP did not say he was a kid. They blow past it in an instant.

My experience says those lessons are about right for a true 1400 player. The real question is whether the OP is really 1400 or whether that is some online inflated rating and if so then these lessons might just be a stretch but could still be good for them.
That said, much depends on the OP’s style of learning. And what their budget is. It might be better to buy selected books that are easier to use and research says most people learn better from books than from a course like this.
Some GM name does not mean the lessons are good. Some GMs play well but cannot teach well. It would be good to check reviews of others who bought and used the course before deciding.

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Why wasn’t Rashid Nezhmetdinov a grandmaster?
He won the Russian championship 5 times, so why wasn’t he a grandmaster?

Rashid Nezhmetdinov, aka “Super Nezh”, was clearly GM strength, having a plus score in the 20 games he played against World Champions, including a plus score against his friend, Tal. He was also a five-time Russian champion (this title predates the Soviet Union, and is not the same as champion of the Soviet Union).
I was a Russian linguist in the Air Force during the cold war (1980-1988), and all of my Russian teachers were “off the boat” as they say, meaning they were natives of the Soviet Union, so we heard many stories about life there, and Nezhmetdinov’s story is not uncommon: Lack of favor.
During his peak years, Nezhmetdinov only managed to play outside of the Soviet Union one time, and he finished second to Korchnoi at Bucharest 1954, which again showed that he was strong enough to be a GM. Unfortunately, strength is not the only factor in getting a title. FIDE has long had in place title rules that were designed to make sure that federations could not manipulate titles, thus you have to play x-number of other titled players, and x-number of players from other countries. So, back then, it was harder to get titles because there were not as many titled players as there are today.
Typically, in the Soviet Union, there were also “favorites”, and they were people, who were Communist Party members, or related to those, who were. If you were not a favorite, you could not travel abroad freely as you can today, and they lived behind what was called “The Iron Curtain”. The Party also worried a lot about players defecting, so in essence, your whole country was a prison of sorts. There were exceptions, who were not Party members, but who were so talented that they could bring the Party great favor and prestige, especially when it made the West look bad. Nevertheless, I read somewhere that Nezhmetdinov was a low-level party member, but he was also not a prodigy as were the Tals and Spasskys of the time.  As great as Rashid Nezhmetdinov was, he had huge flaws in his game, and thus, he would probably never become World Champion, and the top chess players knew it, and thus, the Party did not favor him. If you were not given the opportunity, you cannot succeed. He was also an ethnic minority, a Tatar, which also surely played a role in this.
Personally, I would love it if FIDE would posthumously award Nezhmetdinov the Grandmaster title. He is easily the best player ever not to get the title, during the era of titles. I have since written an email to FIDE President, Arkady Dvorkovich, regarding the possibility of posthumously awarding Rashid Nezhmetdinov the GM title.
For anyone, who does not know of Super Nezh, I suggest you search for some of his games. He has what might be the greatest queen sacrifice ever.
I was asked in comments why black resigned after 33. Ke2, so I added a sample line just showing where to put the white pieces, and how that will eventually lead to an easy win, and Chernikov knew it.
 [Event "Rostov on Don"]
 [Site "Rostov on Don"]
 [Date "1962.??.??"]
 [Round "?"]
 [White "Nezhmetdinov, Rashid"]
 [Black "Chernikov, Oleg L"]
 [Result "1-0"]
 [ECO "B35"]
 [PlyCount "65"]
 [EventDate "1962.??.??"]
 [EventType "game"]
 [EventRounds "1"]
 [EventCountry "URS"]
 [FEN ""]

 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 (33. Ke2 a6 34. c3 Rf7 35. Nb4 a5 36. Nc6 a4 37. a3 Kg8 38. Be3 Kf8 39. Nd4 Rb7 40. h4 Ke7 41. Bf4 d5 42. g3 Kf6 43. Kd3 Rb6 44. Bg5+ Ke5 45. Nf3+ Ke6 46. Kd4 Rb8 47. Ne5 Rg8 48. Bf4+- {and Kc5 next wins}) 1-0

There is an enjoyable agadmator channel video about this game.

"he had huge flaws in his game, and thus, he would probably never become World Champion, and the top chess players knew it, and thus, the Party did not favor him" To you have any source to document this ? I find this very surprising and atypical for the Soviet Sport Committee. Being a Tatar and/or not orthodox enough politically are much more probable factors for travel restrictions and lack of tournament invitation n the Cold War USSR...

@Evargalo I think the point wasn’t “he was held back because of the flaws in his game,” so much as “he was held back for political and ethnic reasons, and while some others have overcome similar handicaps by being that good, he wasn’t quite there.”

If one is not a GM then apparently they did not satisfy the written FIDE rules for getting to be a GM.  Maybe russia had their version of GM titles for players like USA does with USCF.
Was his rating 2500+ ??
Did he play in enough tournaments with enough GMs with enough rounds and score well enough enough times ??
Clearly not since he died in 1974 when the requirements were slightly different, AND he was getting too old to keep scoring well enough.
Back when he may have been that strong they did not award the GM titles like they do now.  The modern system did not start until 1953.
Before 1950, the term grandmaster was sometimes informally applied to world class players. The Fédération Internationale des Échecs (FIDE, or International Chess Federation) was formed in Paris in 1924, but at that time did not award formal titles.
The answer is that he was in the wrong place at the wrong time to get the GM title even though he may have been that strong.
FIDE Titles
The most prestigious titles are granted by FIDE, which is the World Chess Federation. These titles require high FIDE ratings, and the highest titles also require strong performances in tournaments against other elite players. Once granted, FIDE titles are not taken away from players, even if their performance drops. The FIDE titles and their requirements are as follows:
Candidate Master: This title is awarded to any player with an established FIDE rating of 2200 or higher. This is the least prestigious title awarded by FIDE.
FIDE Master (FM): The FIDE Master title is awarded to any player who establishes a FIDE rating of at least 2300. Many international junior tournaments also award the FIDE title to winners; for instance, one may earn the FM title by winning a section at the Pan-Am Youth Games, even if they do not meet the rating requirement.
International Master (IM): To earn the IM title, a player must normally have an established FIDE rating of 2400. However, players must also prove their strength by having sufficiently strong results in (normally) three tournaments against very strong competition. Like the FM title, however, there are potential shortcuts to winning the IM title, such as by being the runner-up at the World Junior Championship.
Grandmaster (GM): The GM title is the most difficult title to earn for any chess player. To become a grandmaster, a player must establish a FIDE rating of at least 2500. Also, he or she must go through the same norms process required of an IM, but with a higher standard required to achieve each norm. Only a few tournaments award a GM title outside of this system; winning the World Junior Championship or the World Senior Championship are two ways in which a player might earn the GM title despite not otherwise qualifying for it.

There is no doubt that he did not fulfill the requirements, but it was a lot more complicated than that. The Soviet Union did not have a "GM" title, but they did have the title "Master of Sport". Assuming that someone did not have an international title, their "Masters" were probably like the average IM, or better.

They had that.  And of course politics is a factor. I suspect they may have had other titles for chess players but maybe not in his timeframe.

Among Soviet players, between 1954 and 1959, only Spassky, Korchnoi, and Tal got the GM title. It was very hard due to not being able to travel abroad, and the lack of tournaments.

And that travel problem was due to politics was it not?

Read my answer, yes it was, but it was a lot more than that. The Soviet Union did not allow its citizens to travel as a rule.

I understand that.  But I thought that  was politics. They did not want unproven hard core commies being corrupted by the decadent lifestyle in the west.

Rashid Nezhmetdinov would be a grandmaster, if not for his extreme minus scores against positional opponents, like Korchnoi and Petrosian. The one problem was that Nezhmetdinov spent too much energy on attempting to attack, so he would neglect his own position in the meanwhile. However, his positional opponents kept the position safe, keeping away attacking chances, and then swooping in to take advantage of weaknesses.
So, if not for his desperation to attack, Rashid Nezhmetdinov would have been a grandmaster.

This surprising answer would need to be documented. Nezhmetdinov overall score against grandmasters was excellent (matching or even beating grandmaster standards), and if he had scored as well against Korchnoi and Petrosian the question in the OP wouldn't be "why wasn't he a GM?" but "why wasn't he a WC candidate ?". Anyway, he still wouldn't have achieved the GM-title without being allowed to play abroad.

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text:
How are online tactic exercises ratings calculated?
There are several sites that give you a tactics rating changing while you solve or fail the exercises.
How do they calculate the problems rating?
Do they use engines to calculate the difficulty or strong players evaluate the difficulty exercise by exercise?

Are there specific sites you are interested in?  different sites may do it differently.

@Michael West I do exercises on lichess, chesstempo and chess.com Lichess may do it using stokfish is my guess, not sure about chess.com as they have a lot of titled staff. Chesstempo may do it also "exercise by exercise"? I was wondering. Your answer says all about how chesstempo does.

Lichess uses the same method as described by Michael.

A typical way to do it is to treat puzzles the same as players and rate them based on whether they "win/lose" and the rating of the "opponent"
ChessTempo has a nice explanation here copied below:

The rating system is inspired by an idea implemented at the Chess
  Tactics Server. CTS treats both problem solvers and the problems as
  opponents with their own ratings and adjusts their rating after
  problem completion (or failure) based on the Glicko ratings system.
For blitz style games, time taken to solve problems is considered and
  an extra bonus is given for problems solved quickly. The solver gets a
  larger rating increase for problems solved quicker than one standard
  deviation from the average time taken for that problem. For problems
  solved faster than average but less than one standard deviation from
  the average, the normal Glicko based adjustment is made. If the
  problem is solved in slower than average time then the Glicko rating
  adjustment is reduced in proportion to how much slower than average
  the problem was solved. Very slow solutions may result in losing
  rating points, however you will never lose more points than you would
  if you simply got the problem wrong.
When calculating the average time taken on a problem, only correct
  solutions are included, time taken from incorrect attempts are not
  used to calculate the average time a problem takes to solve.
It is important to note that after a recent change to time handling in
  blitz mode, time taken after the first move is punished more severely
  than time taken before making your first move. The intention of this
  feature is to discourage 'incremental' guessing to try and solve a
  problem, rewarding users who sum up the situation before making their
  move sequence. Users who prefer to use an incremental approach may
  still do so, however their rating will be lower than users at the same
  level who think out the solutions first.
Normal Glicko adjustments are made for standard ratings with no
  penalty for time taken. Problems marked incorrect cause the rating of
  that problem to increase and the solver's rating to decrease as
  dictated by normal Glicko rating calculations. Normal Glicko
  adjustments are also made for blitz problems that are marked wrong
  (i.e. the time taken in blitz is ignored when making rating
  adjustments for incorrect problems).

I believe that the tactics rating start on 100n rating. After solving puzzles, the change in rating decreases, so that eventually, you'll reach a rating which reflects your accuracy.


text:
Who did Kasparov call a talented amateur?
I heard that Kasparov called some strong player a talented amateur? Who was that? Thanks.

I will answer in the first line of the next paragraph, but there is a lot of history that happened right around the time Kasparov made this comment, so I will add in some of that too.
At the Tilburg tournament in November 1997, Kasparov was not known for holding his tongue, and he called Grandmaster Shirov, who was 2700 and 8th in the world, a "talented amateur". Shirov did not appreciate the remark. Kasparov’s comment is ironic since it was only about a year later that Shirov would upset Kramnik in a match (5.5-3.5) to win the right to play Kasparov for the PCA (Professional Chess Association) World Championship in 1998, but the match never took place because there was no sponsor since Intel, and later Linares organizer Luis Rentero, pulled out, and the money could not be secured. The PCA collapsed. Shirov was probably not without blame as it is alleged that he refused to play since his cut was too small.
My opinion is that if you are not champion, you should play, and if you win, then you have more leverage…get paid big down the line. That said, it is a big stretch to think that Shirov would have beaten Kasparov anyway as Shirov was Kasparov’s “customer”, meaning that Kasparov beat him like a drum throughout their career. The lifetime record was 16 wins, 15 draws, and zero losses for Kasparov.
After this happened, a new sponsor, BrainGames.com, was eventually secured for a Kasparov match, but unfortunately, the sponsor tried to sign Anand to play Kasparov, but this fell through too. Shirov was naturally upset that he was not signed, and called Anand a “pickpocket”, and he felt that Kasparov had to play him before he played any other matches. It turned out that since even that match never took place, Kasparov ultimately played Kramnik in 2000, and well, we know how that turned out: Kramink, a heavy underdog, used the Berlin Defense to the Ruy Lopez, and won by a score of 8 1/2–6 ½. Anand would go on to win the separate FIDE World Championship knockout event that year as Kasparov had previously broken away with the classical title in 1986.

What happened to Shirov is really unfortunate. Kramnik got paid for losing the match, but Shirov only got a chance to play Kasparov (with much larger payoff, but it never happened). Original prize fund for Kasparov - Shirov match was around 2 million dollars. Shirov was offered match with prize fund of $650,000, with I think $200,000 for 2nd place, which is what Kramnik got paid for losing to Shirov, iirc. Shirov rejected, but he did not realize that it was the last offer. In the end Shirov ended up with no money and no match.

I thought it was called "client" not "customer".


text:
Why did Fischer play 17.c4 here?
Why did Fischer play 17...c4 here?
[fen "r4rk1/1q1n1pp1/4b2p/p1pp4/8/Q2NP3/PP2BPPP/R4RK1 b - - 0 1"]

Doesn’t it make the bishop e6 a lot worse? I would have played rfb8 instead, but I am not Fischer.

Every move has pros and cons. Move a pawn, for example, and you gain space, and control squares; but you also weaken squares. The trick is to accurately determine if you will be able to use your pros better than your opponent can use your new-found weaknesses against you. Always remember that a “weakness” is only a weakness if your opponent can get at it, and use it against you.
In this position, 17…Rfb8 is also a very good move, but Stockfish definitely prefers c4. After 17…c4, Fischer decided that the immediate pressure on b2 was more important than making the bishop worse. In addition, when the Nd3 moved to f4, from there, it really could only trade itself off for that bad bishop in most situations. As in the game, because white did not take immediately on e6, the bishop went to f5, and deprived the white rooks of the b1 square, and thus, a method of defending the pawn on b2.
It was almost inevitable that white would lose a pawn. As it was played, after 21…g5, white felt compelled to give up the piece altogether seeing the variation 22. Nh5 Ne4 23. Rc2 Qb4 paralyzing white.
I do not know if you are reading “My 60 Memorable Games”, but this is game 34 in that book, and the game was titled, “Hanging pawns unhung”. Lastly, it is interesting to note that Fischer thought that the best move was 19. Nxe6 getting rid of the “bad” bishop, giving the variation: 19. Nxe6 fxe6 20. Bg4 Ra6! 21. b3! cxb3 22. axb3 Qxb3 23. Qe7 Nf8 24. Ra3 Qb4 25. Qxb4 Rxb4 26. Be2 Ra7 27. Rfa1 a4 28. Bd1 “with good drawing chances”, but 21…Qb4! Stopped the queen from taking up the active position deep in the black camp, and threatens cxb3 with a strong passed pawn, since it exposes an attack on the hanging Bg4. Per Stockfish Qxb4 is forced, and is probably close to lost in my opinion due to the incredibly weak white queenside.
 [Event "Interzonal-05"]
 [Site "Stockholm"]
 [Date "1962.03.04"]
 [Round "22"]
 [White "Bertok, Mario"]
 [Black "Fischer, Robert James"]
 [Result "0-1"]
 [ECO "D59"]
 [PlyCount "62"]
 [FEN ""]

 1. d4 d5 2. c4 e6 3. Nc3 Be7 4. Nf3 Nf6 5. Bg5 O-O 6. e3 h6 7. Bh4 b6 8. cxd5 Nxd5 9. Bxe7 Qxe7 10. Nxd5 exd5 11. Be2 Be6 12. O-O c5 13. dxc5 bxc5 14. Qa4 Qb7 15. Qa3 Nd7 16. Ne1 a5 17. Nd3 c4 18. Nf4 Rfb8 19. Rab1 (19. Nxe6 fxe6 20. Bg4 Ra6 $1 21. b3 $1 {Fischer's !} cxb3 (21... Qb4 $1 {Not letting the Qa3 get active.} 22. Qxb4 axb4 {And white is in huge trouble.}) 22. axb3 Qxb3 23. Qe7 Nf8 24. Ra3 Qb4 25. Qxb4 Rxb4 26. Be2 Ra7 27. Rfa1 a4 28. Bd1 $15) 19... Bf5 20. Rbd1 Nf6 21. Rd2 g5 22. Nxd5 (22. Nh5 Ne4 23. Rc2 Qb4 {Winning positionally.}) 22... Nxd5 23. Bxc4 Be6 24. Rfd1? Nxe3! 25. Qxe3 Bxc4 26. h4 Re8 27. Qg3 Qe7 28. b3 Be6 29. f4 g4 30. h5 Qc5+ 31. Rf2 Bf5 0-1

Every move has plusses and minuses.
Fischer does not want to be tied down defending the pawn which would tie up his pieces.
c4 attacks the horsie, and blocks whites bishop making it less good now.
it allows for black to attack on b2 by moving his rook.  it also opens up c5 for the horsie to use at some point.
it attacks b3 so white will have trouble moving the pawn up and defending it after its capture.
overall it is a good positional move improving blacks chances.


text:
How did Timman decide on d5 in this position?
In Gheorghiu-Timman 1982, how did Timman decide to play 34…d5? It seems like an amazing move to find.
 [FEN "2r5/p1r2b2/1p1p1k1p/PP2ppp1/2P2P2/3KP1P1/2RN3P/2R5 b - - 0 1"]

 1... d5

as written that would be strictly opinion.  better to restate as what factors drive the choice of the next move.

In this position, black clearly is better with heavy pressure down the c-file, but it is clear that c4 is also well defended, and that black cannot bring any additional pressure on c4 except with d5. So, can black do anything else like try and infiltrate with Kg6-h5? I ran some logical lines with Stockfish, but they are labyrinth-like, and while it is clear that black is still the one pushing, nothing was clear. In those lines, black also has to be on the lookout for possible e4 attempts by white, and also axb6 axb6, Ra1-a6 lines that can gain great counterplay should black win b6, and start pushing the b5 pawn.
d5 is a way to increase the advantage, and clarify the position. Timman also saw that the white knight was no match for the good bishop, and better black king position. Gheorgiu should have avoided that at all costs.
 [Event "Olympiad-24"]
 [Site "Valetta"]
 [Date "1980.11.25"]
 [Round "5"]
 [White "Gheorghiu, Florin"]
 [Black "Timman, Jan H"]
 [Result "0-1"]
 [ECO "E32"]
 [WhiteElo "2605"]
 [BlackElo "2600"]
 [PlyCount "106"]
 [EventDate "1980.11.20"]
 [EventType "team-swiss"]
 [EventRounds "14"]
 [EventCountry "MLT"]
 [WhiteTeam "Romania"]
 [BlackTeam "Netherlands"]
 [WhiteTeamCountry "ROU"]
 [BlackTeamCountry "NED"]
 [FEN ""]

 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Qc2 O-O 5. a3 Bxc3+ 6. Qxc3 b6 7. Bg5 Bb7 8. e3 d6 9. f3 Nbd7 10. Bd3 c5 11. Ne2 Rc8 12. O-O Ba6 13. b4 cxd4 14. Qxd4 h6 15. Bxf6 Qxf6 16. Qxf6 Nxf6 17. Rac1 Nd7 18. Rfd1 Ne5 19. b5 Bb7 20. f4 Nxd3 21. Rxd3 Rfd8 22. Rdc3 Rc5 23. Nd4 Rdc8 24. Nb3 R5c7 25. a4 Bd5 26. Nd2 f5 27. Kf2 Kf7 28. g3 Ke7 29. Ke2 e5 30. Kd3 Be6 31. a5 g5 32. Nb3 Kf6 33. R3c2 Bf7 34. Nd2 d5 (34... Kg6 35. axb6 axb6 36. Ra1 $11) 35. fxe5+ (35. axb6 axb6 36. Ra2 $2 dxc4+ 37. Kc3 Rc5 {And black is too fast.}) 35... Kxe5 36. cxd5 $2 {Going into the bishop versus knight ending was clearly hopeless.} (36. axb6 $1 axb6 37. c5 $1 Rxc5 (37... bxc5 38. Nf3+ Kf6 39. Kd2 Bh5 40. Nd4 Ke5 41. Nc6+ {And if black hopes to win, he will need to sacrifice the exchange here.}) 38. Rxc5 Rxc5 39. Rxc5 bxc5 40. Kc3 Kd6 41. Nb3 c4 42. Nd4 Kc5 (42... Bg6 43. Kb4) 43. Nxf5 $11 {This leads to an ending that is possibly holding, but would have been very hard to find at the board.}) 36... Rxc2 37. Rxc2 Rxc2 38. Kxc2 Kxd5 39. axb6 axb6 40. Kc3 Bh5 41. Nb3 Be8 42. Kb4 Ke4 43. Nd2+ Kxe3 44. Nc4+ Ke2 45. Nxb6 f4 46. gxf4 gxf4 47. Nd5 f3 48. Nc3+ Ke1 49. Ne4 f2 50. Nxf2 Kxf2 51. Kc5 Bd7 52. b6 Bc8 53. Kd6 h5 0-1

It is impossible to know what is in the mind of the person playing.
Based on the position, my instinct as if playing blitz,  it looks like white wins a pawn or ties down all of whites pieces so the black K can raid the Qside pawns.
A computer analysis may find differently especially if it can find a better move to start with.
Not sure that it is that  aamazing a  move to find as it seems rather obvious and takes little analysis to say go ahead and do it.


text:
I was playing a tournament and some kids were talking about the game in a foreign language
I was playing and I am pretty sure that my opponent was talking about the game with his friend in another language. I don’t speak the language, but you can tell. What should I have done?

How old was your opponent? The repercussions for a 10-year old might/should be different than for a 40-year old.

Your opponent was talking with his friend while the game was still going on? Or afterward?

First, you should inform the tournament director, and let that person handle it. There is a parental instinct that makes me want to just take the kid aside, and say something privately first, but since that can be misconstrued, do not do that, and let the TD handle it. I am sure that they will mention it, or warn the kids, and hopefully it will be done with.
I speak Russian, and in times gone by, I would hear some of them discuss games that were not mine, and it was not so much about specific calculations, but still. Thankfully, it was not common, but it still violates the rules, and needs to be dealt with. In my case, they were always adults, who should have known better. In your case, you have kids, who often just have not been taught well enough yet, and hopefully a stern word of warning will end this before it is evolves into intentional cheating.
Playing kids is hard enough: To have to play two of them in tandem is for the birds. :)

huh?  you cant discuss other games ?  since when ?

I am used to playing under USCF rules, and it has always been prohibited: 20I. Discussion of games. Players should not discuss their games in progress with anyone; this may lead to penalties under 20E, Soliciting or using advice prohibited. The director has the option of banning all talking in the tournament room, even if not loud enough to be disturbing. See also 1C2, Director discretion; 20K, Penalties; 21F2, Facts are agreed upon; and 21K, Use of director’s power. They typically ban all game discussion so there is no ambiguity. If you are in another room, it is generally fine.

I was talking about discussing other games while in the tournament hall. If nothing else, one of the players may overhear you, or notice your excitement, or other facial expressions, and realize something is up.

never was at a tournament where some people did not discuss games in the playing area.  the bigger and more formal the less discussion but still it happened.  one GM came up to look at my game against lombardy and shook his head up and down.  others actually talked about other games away from  their table.

You are talking about a long time ago. It has been a no-no for a long time now.

and you say that now  absolutely everybody say nothing to anyone the whole time?   even at small local tournaments ?

I have only played in a few tournaments, but have never heard anyone discussing games. I play 'postal' now and still need to be careful to not discuss my games in progress.

They may not always do it, but it seems common that they do discuss when they have the opportunity EG waiting for opponent who is taking a long time and they are at the snack bar area.  Rarely do I see them offer advice as to moves in their games but they do discuss what some other player might do in the current position.

Hi Liam and welcome to chess.stackexchange. I am sorry that you had this experience. If this tournament was played under FIDE rules, then the following articles are directly relevant:

11.3.1 During play the players are forbidden to use any notes, sources of information or advice, or analyse any game on another chessboard.
11.5 It is forbidden to distract or annoy the opponent in any manner whatsoever.
12.7 [...] Spectators are not allowed to interfere in a game. The arbiter may expel offenders from the playing venue.
12.2 The arbiter shall:

12.2.1 ensure fair play,
12.2.2 act in the best interest of the competition,
12.2.3 ensure that a good playing environment is maintained,
12.2.4 ensure that the players are not disturbed,
12.2.5 supervise the progress of the competition,
12.2.6 take special measures in the interests of disabled players and those who need medical attention,
12.2.7 follow the Anti-Cheating Rules or Guidelines

You should therefore at the time call the arbiter and explain the situation so he can take the corrective steps.
The arbiter should stop the clock (although the player has the right to do this prior to calling the judge too). The judge has absolute discretion under the laws, to come to the best solution. A wide number of different circumstances can have led to the complaint, with varying levels of penalty appropriate, and different clues are available. If cheating is suspected then a substantial interruption may be required for investigation

an what would the TD do ?   the one key move to help the kid win may already have been given to him..  how can they make it fair after the fact?

Thanks Edwina - am adding the response to my answer.

By way of comparison, in international magic the gathering tournaments, i’ve come across this kind of behaviour fairly often. It’s a game where there is some dialogue between the players as a matter of course, any communication from outside the game is banned.  Normally I would ask for the communication to stop and (on the very rare occasion when it didn’t happen) immediately call a judge. Chess does not have such a natural window for dialogue between the two players, so I would call the arbiter much sooner.

Please do no use codeblock for things that are not actually code. Quoteblock should be used when directly quoting other sources. Marking edits with meta commentary is not necessary, a post should be edited to the best form of itself without demarcation between versions - that's what post histories are for.

(1) Someone edited out the welcome sentence at the beginning of my answer. I disagree that this is inappropriate and I have restored it. (2) Someone removed an “EDIT:” indication. Although in principle one can investigate the edit history, that is disruptive and in some cases it is best to show the sequence of logic explicitly, especially since the sequencing of edits and comments is not obvious. This is not really the case here so concur with the removal of “EDIT:” (3) I will try to use quoteblock not codeblock in the future - that explains issues I had with line feeds. Thanks all

@Laska, general Stack Exchange policy is to not signal edits. It's a question and answer site, not a conversation forum - answers should always reflect their best form as if it had always been that way. Furthermore, as it is not a conversation form, chatty preambles are also discouraged. Your answer should be useful to more people than just the original poster, so addressing the original poster in a conversational manner is not part of the Q&A format (because welcoming Liam is not useful to future readers).

This is a small group which would still be beta if that status still existed. I have noticed over the last few years many newcomers to the chess forum being scared off by frosty overbearing receptions. I believe a touch of warmth is important to all new readers. If the chess moderators feel my approach is inappropriate than that might be a different matter. I hardly feel that a line of greeting distracts from the answer. Welcome to yourself T.J.L. and please do participate creatively in this forum


text:
Your time is up on an online correspondence game but your oponnent has only his king; is it a draw?
If your time is up on a timed game, but your opponent has only a king, the game is drawn.
Does this rule apply to online correspondence games?

The FIDE laws of chess do not apply as they only "cover over-the-board play" (very first sentence of the introduction), which excludes both correspondence and online games.

If you provide me your chess.com name we can try it out.

@Michael West this is my profile. The server gives draw

That seems clear.  No need to test then?  You may wish to answer your own question here

Note: This was answered before the OP edited the question, and specified it was an online competition.
According to ICCF (international) rules, yes, it is still a draw.
6.7 Except where one of  the Articles 5.1 or 5.2 applies, if a player does not complete the prescribed number of moves in the allotted time, the game is lost by the player. However, the game is drawn, if the position is such that  the opponent cannot checkmate the player’s king by any possible series of legal moves.
The USCF rules are more convoluted. First, there is a special rule 11 in national events that if someone oversteps the time limit, they are not forfeited, but rather penalized five days reflection time on the succeeding 10 moves/30 day time control. They lose the second time this happens. (Plus there are entire sets of rules for specific national events linked on that page)
Otherwise, they also follow the traditional USCF rules of chess, so yes, it would also be a draw in that case too.
14D. Insufficient material to continue. The game is drawn when one of the following endings exists as of the most recently determined legal move, in which the possibility of a win is excluded for either side.
14D4. No legal moves leading to checkmate by opponent. There are no legal moves that could lead to the player being checkmated by the opponent.

@Universal_learner I would imagine that all servers also award a draw since they are programmed that way for other time controls.

Thanks they finally answer at chess.com and the server gives draw. https://www.chess.com/forum/view/help-support/loosing-on-time-on-correspondence-where-my-oponnent-has-only-the-king


text:
Chess.com's daily problem-Why doesn't 1...Nf8 win the Nh7?
Shouldn't 1...Nf8 win here too? Why not?
[FEN "r2qk2r/pp1nnp1N/4p1pQ/3pP3/4b1PP/P1B5/1PP1B3/R3KR2 b Qq - 0 1"]

1...Nf8??

You could have just put the position in an engine and it would have told you. You don't have to ask the StackExchange about that.

It loses due to Nf6#.

@SubhanKhan Not everyone is that experienced, or has the tools that you may have, or know how to get them...or even that they exist.

What is the full problem?

@John If it is beyond my answer below, what do you mean, what is the full problem? I showed the entire solution below. It is the sub-variation starting with 1...Ng8!

The title should read "1...Nf8," or else the post should be able to specify that it's Black's move, because I was momentarily very confused as to why White should play 1.Nf8.

Frankly, you overlooked a major detail...Nf6+ in reply is mate. It is important to notice your "opponent's" moves too.
 [FEN "r2qk2r/pp1nnp1N/4p1pQ/3pP3/4b1PP/P1B5/1PP1B3/R3KR2 b Qq - 0 1"]

 1... Nf8 $4 (1... Ng8! 2. Qg7 (2. Nf6+ Qxf6 $1) 2... Qxh4+ 3. Kd2 Qxh7) 2. Nf6#

Nf6 is not only mate, but also wins the rook on h8 due to the discovered attack ;-). Unlike in the line Ng8, black does not have the reply Qxf6 here...


text:
Is chess a good game to fight against gambling addiction?
I read a couple of poker books and I thought I could win, which was not the case.
Fortunately for me I have a decent chess level, 1930 in rapid, and I simply changed poker books for chess books and returned to the club. I have not lost a lot, but I realized if I don't win money why play something I enjoy less than my favourite game since I was a child.
As the game is helping me not to gamble, I wonder if it is documented from a medical point of view similar cases where chess helped.

I guess anything you enjoy helps against an addiction; running, music, food could work too. Unless that thing becomes an addiction itself ...

@Glorfindel. Chess is also a bit adictive but much more less. Maybe you can say chess acts as a less harmful sustitutive.

Its worth noting that it is also possible to gamble/bet on chess games (or pretty much anything in life) so perhaps it is not the game itself that is the substitute but the substitute is that it is far less likely to wager money on chess games.

I don't know about chess. At least one local bridge master, not playing for money, used to have a cash gambling problem with poker.

I think the game per se is more adictive. I have been playing a couple of months and it is AJKQ raise 2759 fold,.thousands of hands...very repetitive. And you finish by geting tired and playing bad->gambling. you have not minutes to act as on chess. Chess mouvements can be automathic if you playing a known openning, but I find chess less adictive for money but for the game itself too.

I have seen plenty of people, who are addicted to chess, as it can become very time consuming if you take it seriously. So yes, it could easily help people swap an addiction that most would see as potentially more detrimental for one that is more healthy.


text:
How can I use stockfish to find good moves, instead of just bad moves?
After playing on lichess.org I have been reviewing my games as follows:

Ask for a computer evaluation (Stockfish)
Look at the graph and investigate any wild swings in computer analysis
Try to understand why a particular move was a blunder

While this seems to work, it's a very negative approach as it doesn't seem to find any good moves that I've made.  For example, at my level (Blitz ~1230) I might win a game because I laid a trap which my opponent failed to see.  Stockfish of course sees through the trap and the evaluation shows I made a suboptimal move even though against this particular opponent it resulted in me winning a piece.
Is there any way to find good moves that I made, rather than just non-mistakes?

At your level, you should just forget about Stockfish. It doesn't really help you. The mistakes it'll point out are basically piece-dropping. You don't need a computer to expalin you why losing a rook in exchange for nothing is bad, and to help you in the future you'll need to be able to see those things by yourself

Related: Why does Lichess only tell me my “inaccuracies”, “mistakes”, and “blunders”, and not e.g. my “brilliancies”?

Sorry, computer engines are not designed to think like a human. It's a machine, it's written to play strong chess. There is no intelligence in there to think like that.
The "good moves" you mentioned were actually bad moves at Stockfish's level.

+1. From Stockfish's perspective, there are NO "good" (creating some advantage on their own) moves whatsoever - merely "not bad"(not losing some advantage) ones. You win if your moves are less bad than your opponent's.

Is there any way to find good moves that I made, rather than just non-mistakes?

Actually, in most cases, it's doing this already. The reason your moves aren't showing up is probably that they're not actually good moves!

the evaluation shows I made a suboptimal move even though against this particular opponent it resulted in me winning a piece

The computer doesn't care about the "narrative" of the game. It looks at the position and evaluates the moves that are available.
I recommend picking one move per game that the computer shows as "non-optimal" and asking yourself: What factors in this position do I need to notice before I'd make this move?
To answer this question is usually very difficult. There is something about the position that you've missed or misunderstood, and it may take you a few minutes (probably more than 5, it has sometimes taken me more than an hour) of investigation before you figure it out. That is how you use Chess computers. They're a tool that can help you evaluate a position. They're not a tool to reassure you that a sub-optimal, albeit romantic, move was actually good.

it doesn't seem to find any good moves that I've made

You are expecting too much is the real issue here, so don't be so hard on yourself. First, and I do not say this to be mean, but your level of play is going to contain mostly bad moves, but they look that much worse because you are being evaluated by a silicon beast. Keep in mind that Stockfish is FAR superior to the World Champion, so it is going to find better moves on almost every move.
Please try not to take the evaluations so hard. Look at them, but stop beating yourself up over them. I have been a USCF Master for well over 30 years, and Stockfish thinks I am an idiot too. :)
That said, focus on more tactics problems. I was at the high school club I run today, and a few are probably about the same strength as you are, and even one that is better, but the amount of tactical errors is astounding, so keep working on those.
I recommend trying to do 50 per day all within one topic, like pins, skewers, or deflection, for example. Spend no more than two minutes per problem. If you are going to do them online, REALLY try to avoid the mouse until you have really solved it in your head, and are not just moving a piece, and hoping that the computer confirms your "guess". The key is solving not guessing.

If after making a move the engine’s score for the position is virtually unchanged - it’s good move!

Run Stockfish in multi-PV mode. This makes Stockfish suggest multiple moves. If the move you chose is preferred by Stockfish to others, then it's a "good move".

Not really. Even the second multipv can be an objectively a bad move. It all depends on the position.

@HelloWorld or one can interpret it as "there's only one good move in the position", and making that good move is still making a good move.


text:
Understanding Carlsen's resignation in the rook and pawn endgame vs MVL
Why did Carlsen resign in the position shown below? (blitz game played in the London Chess Classic GCT Finals)
Can't white help the pawn queen after Ke3 and Kd3 then Kd4? I must be missing something.
[Title "Magnus Carlsen-Maxime Vachier-Lagrave, London Chess Classic GCT Finals, London England 12/02/2019"]
[FEN ""]
[startply "108"]

1. d4 Nf6 2. Nf3 g6 3. Nbd2 d5 4. b3 Bg7 5. Bb2 a5 6. a4 O-O 7. e3 Bf5 8. Be2 Nc6 9. O-O Nb4 10. Ne1 Ne4 11. c3 Nxd2 12. Qxd2 Nc6 13. Nd3 e5 14. Nxe5 Nxe5 15. dxe5 Bxe5 16. Rfd1 Qd6 17. Ba3 c5 18. Qxd5 Qxd5 19. Rxd5 Bxc3 20. Rad1 Bb4 21. Bxb4 cxb4 22. Bc4 Be6 23. Rb5 Rfd8 24. Rd4 Rac8 25. Rxd8+ Rxd8 26. Kf1 Bxc4+ 27. bxc4 Rd2 28. Rxb7 Ra2 29. c5 Rxa4 30. Ke2 Ra3 31. c6 Rc3 32. c7 Kg7 33. Ra7 b3 34. Rxa5 Rxc7 35. Rb5 Rc2+ 36. Kf3 b2 37. Rb6 h5 38. h3 Kf8 39. g4 h4 40. g5 Ke7 41. e4 Kd7 42. Ke3 Kc7 43. Rb5 Kc6 44. Rb8 Kc5 45. f4 Kc4 46. f5 Kc3 47. Kf4 Rg2 48. fxg6 fxg6 49. e5 Re2 50. Rb6 Kc2 51. Rc6+ Kd1 52. Rd6+ Kc1 53. Rc6+ Rc2 54. Rb6 Rc4+

https://www.chessgames.com/perl/chessgame?gid=1983200

Intuitive plan
Notice that black's last check is pushing the white king one row away from their passed e-pawn. Once black promotes the b-pawn, white will have to give up the rook for it. After which white's king is simply not in position to cover the advance of the e-pawn and therefore additional tempi will have to be spent with king moves to try and reach the pawn, during which the rook can first simply capture white's h-pawn and only then sacrifice itself for the e-pawn. Then black's h-pawn promotes and wins trivially. Now let's see how all this pans out concretely (no matter how strong the intuition might be, in endgames one must always primarily rely on concrete calculations in order to realise whether our ideas or plans can actually be optimally implemented).
Annotated diagram
 [title "A simple continuation showcasing why white is lost here"]
 [fen "8/8/1R4p1/4P1P1/2r2K1p/7P/1p6/2k5 w - - 0 1"]

 1. Ke3 b1=Q 2. Rxb1+ Kxb1 3. Kd3 (3. e6 {blunders the e pawn away} Rc6 4. e7 Re6+) Ra4 4. Ke3 {again, the pawn advance would simply leave it hanging, so white has to make king moves while not allowing black to get behind the pawn} Ra3+ 5. Kd4 Rxh3 6. e6 Rh1 7. Kd5 h3 8. e7 Re1 9. Kd6 Rxe7 {though black doesn't even have to sacrifice the rook here, but it's simply a practical way of going about it, and in-line with our original plan} (9...h2 {much more accurate continuation as we can in fact keep our rook since white's tactically losing their queen immediately upon promotion, in fact you might find this line easier to calculate} 10. Kd7 h1=Q 11. e8=Q Qd5+ 12. Kc8 Rxe8+) 10. Kxe7 h2 {and it's easy to judge that black's winning here since the promoted queen is well in time to get to white's promotion square g8 and then simply bring the king over. I'll include this sequence} 11. Kf6 h1=Q 12. Kxg6 Qb7 {cutting off the king from accessing the 7th row} 13. Kf6 (13. Kh6 Qf7 14. g6 Qg8) Qh7 14. g6 Qg8 {and now black simply brings the king and wins the pawn}

thank you. I liked your answer, but I hope you do not mind that I accepted Phishmasters answer. It was even easier that way.

In short, the plan you proposed is possible, but it is just too slow, even if black allows it, which is not mandatory. If black permits it, here is a simple win that, although I checked it with a computer, I could see it in my head fairly easily, which means those two could see it that much more easily.
 [FEN "8/8/1R4p1/4P1P1/2r2K1p/7P/1p6/2k5 w - - 0 1"]

1. Ke3 b1=Q 2. Rxb1+ Kxb1 3. Kd3 Rc8 $1 4. Kd4 Kc2 5. Kd5 Kd3 6. e6 Ke3 7. Kd6 (7. Ke5 Re8 8. Kf6 Kf4 9. Kf7 (9.Kxg6 Rxe6+ 10. Kh5 Kg3-+) Ra8 10. Kxg6 Rg8+ 11.Kf7 Rxg5 {and Re5 next.}) Kf4 8. e7 Kxg5 9. Kd7 Ra8 10. e8=Q Rxe8 11. Kxe8 Kf4 12. Kf7 Kg3 13. Kxg6 Kxh3 14. Kf5 Kg3 15. Ke4 h3 16. Ke3 h2 17. Ke2 h1=Q $19

As I was checking my line with a computer, another line it suggested contained a common valuable theme in some rook endings where the king is cut off on a rank, but the pawn is not advanced enough: If the pawn moves forward, you can attack it with the rook, it advances, and then you can get behind it, and take it the next move.
After 3...Ra4!, there are only two plans: To move the king around until black gets close to g2 with the king, or to advance the pawn, which shows the common theme I mentioned.
 [FEN "8/8/1R4p1/4P1P1/2r2K1p/7P/1p6/2k5 w - - 0 1"]

 1. Ke3 b1=Q 2. Rxb1+ Kxb1 3. Kd3 Ra4 {What can white do here? There are only two plans: Move the king back and forth until black brings the king to g2, or to advance the pawn eventually.} 4. e6 (4. Ke3 Kc1 5. Kf3 (5. Kf2 Re4 $19) 5... Kd1 6. Ke3 Ke1 7. Kf3 Kf1 8. Ke3 Kg2 $19) 4... Ra6 5. e7 Re6 $19

And lastly, moving the king away from its own pawn via 4. Kc3 leaves it undefended and susceptible to 4..Re4 and 5..Rxe5

(Is something missing in "was very contained a valuable theme"?)

@PeterMortensen Thanks. Sometimes editing and combining two sentences, I have been known to make a mistake....combined with middle-aged eyes. I corrected it. Please let me know if it still does not seem clear to you.

It's not immediately obvious to me what happens if White tries to get to the g6 pawn as soon as possible (with something like 7.Ke5.

@JiK I will admit that it makes the computer line with 3...Ra4 look that much easier, but it is still it is pretty easy. 7.Ke5 Re8 8.Kf6 Kf4 9.Kf7 Ra8 10.Kxg6 Rg8+ 11.Kf7 Rxg5 and Re5 next. I will add this to the variations. Good catch. The second plan kills all counterplay, and is preferable.

While it may appear that White can whisk around Black's rook and promote, there is a indeed problem that you have missed: Black can promote first!
White's king is currently in check from Black's rook, so the monarch must be moved to either the f3 or e3, cutting the king off from half of the board.
Since White lost a tempo moving their king, Black now promotes their passed b-pawn to a queen, threatening a variety of mating sequences. White must give up their rook for the newly born queen, a practically forced move. After Black recaptures, they are a full rook up. White has a passed pawn, but it will be soon be taken down by Black's superior firepower, cementing a total loss for White and a victory for Black.
Here is a sample game, Stockfish generated at Depth 53, that shows how Black will be able to systematically suppress and restrict the White king to eventually win.
[FEN "8/8/1R4p1/4P1P1/2r2K1p/7P/1p6/2k5 w - - 0 1"]

1. Kf3 b1=Q 2. Rxb1+ Kxb1 3. e6 Rc6 4. Kg4 Rxe6 5. Kxh4 Re4+ 6. Kg3 Kc2 7. Kf2 Kd2 8. Kf3 Kd3 9. Kg2 Ke3 10. Kg3 Ke2 11. Kg2 Re3 12. h4 Re4 13. Kg3 Ke3 14. h5 gxh5 15. Kg2 Rg4+ 16. Kh3 Rxg5 17. Kh4 Kf4 18. Kh3 Rg4 19. Kh2 Ke3 20. Kh1 Kf2 21. Kh2 Rh4#

I hope that this helps you understand the endgame better!

This helped but didn't go into the plan trying to queen the E-pawn.

This line does show trying to queen the e-pawn with e6.  What other ideas are there to try to queen?

Imagine there'd be no other pawns on the board, except for the b2 pawn and the e5 pawn. Then ask yourself the question: is black's position won? If the answer is yes, there is no need for calculation, right?
The answer is yes, because of an elementary (yet crucial) manoeuvre: keeping the black rook on the fourth rank, thereby cutting off the enemy king. This is seen very often in rook vs. pawn endings and important to bear in mind.
Explanation
So black promotes the pawn and white plays Kd3 after. Then black goes Ra4. After e6 black plays Ra6 and white can not defend the pawn and thus loses it.


text:
Looking for an opening that had been wrongly evaluated for years
I'm looking for an opening I saw in a book (not a chess book). The opening was about 10 moves long, and the author stated that the evaluation after the last move shown had been considered for many years in many chess books as "black has a slight advantage", but later it had been shown that white could checkmate in 1 move.
Additional information: the book I read was written by Martin Gardner. It was not a chess book, but possibly a collection of his Scientific American columns, published in the 60s - 80s. This chess opening was (if I remember correctly) an example in a chapter devoted to puzzles and problems, unrelated to chess, that had been published with a wrong solution, or with a solution that later had been improved.

Even as long ago as the 90s, opening books were usually computer-checked for accuracy, so it would be unlikely for an opening book of that time to not account for a mate in 1 ... That means that the book you are thinking of is probably older than that, and written without computer-checking.

@ZubinMukerjee: I have edited the question to clarify some details about the book and the openning.

My guess is that this is not a theoretical opening. No way that Fischer et al would miss mate in one in a known position. I think this is probably one of those artificial puzzles which requires a number of nonsensical moves from both players to get an "interesting" position.

What does it mean for an opening to be "about 10 moves long"?

@David: I tried to mean that, from what I recalled, white's first 10 moves were given, but there could be 9 or 11 moves. As the answer shows, there were only 9 moves

Maybe Martin Gardner was writing about this story. I'm quoting from p. 95 of Irving Chernev and Fred Reinfeld, The Fireside Book of Chess, Simon and Schuster, New York, 1949. (Of course they gave the moves in descriptive notation.)

In the eighth edition of a popular manual by Dufresne and Mieses, the following line of play is given:

[FEN ""]

1.d4 d5 2.c4 e6 3.Nc3 c5 4.Nf3 cxd4 5.Nxd4 e5 6.Ndb5 d4 7.Nd5 Na6 8.Qa4 Bd7 9.e3 Ne7

In this situation, the authors' comment is, "Black has the superior position." What the analysts seem to have overlooked is that White can mate on the move!

I'm guessing Kt-B3 was somehow typoed into Kt-K2.

I've removed my answer because this looks much closer to what the OP is looking for. +1

@bot: Yes, that's exactly what I was looking for.


text:
How to start learning theory? (1850 Elo)
I have been playing online chess (lichess.org) for three years at the rate of a few hours a week and I recently reached the score of 1850 Elo points in bullet mode.
So I want to take more seriously chess and in particular to learn the theory.
To tell you the truth, I've never done any tactical exercises, I don't know any openings or complex finals.
How do I go about it? I am not at all afraid to use books.

Is bullet the only mode you play? Because if so, I'd seriously consider playing slower time controls if I were you; the bullet mode is not very helpful for improving your overall chess strenght imo, since it relies heavily on the ability to mouse-jockey and play unexpected rather than good moves to make your opponent use more time on the clock.

Yeah, it's the only mode I play, but I feel like you have some unfounded assumptions. It's not really a question of what will move the mouse the fastest, I still have a few seconds per move. But thanks for the advice.

I would give Dereque Kelley a try: https://www.youtube.com/channel/UCa2Ezoefyh5Gm9gXwg0kCdA. He explains openings ideas from the high level. He generally aims at beginner level players, but it might be a good starting point.

I'll take a look at it, thank you

Learning theory involves some memorization of moves, but it's also important to understand the core ideas behind the moves. With these ideas, you can figure out what to play in novel situations not covered by the theory you've studied (or if you end up in a position that you forget).
There are different ways to study using an opening book. If you have a program like Chessbase, you could input the moves given, and also annotate in what you think the main ideas are. A good chess book will also take the time to explicitly explain the main ideas; some don't, which will require you to think on your own why a move was given. If you don't have Chessbase, I suppose you could go through the moves on an actual board, and jot down your notes somewhere (like in Word or a notepad).
If you're trying to get better at a new opening though, I'd suggest playing something longer than bullet - try at least 5 0. You want time to think about the position and apply the ideas (and moves) you've learned.

The way I learned chess, was by playing over games from books by great players and going over the analysis they wrote between moves. I think I have over 500 chess books.
I played over all games of Kaprov, Fischer, Alekhine, Capablanca, Smyslov, tal, etc.. and tried to guess what the next move should be before looking at it.
For learning how to think in chess, I found the book "Think Like a Grandmaster" by Alexander Kotov really good and taught me how to organize my chess thoughts during games and most important, how to be efficient in doing it. Sometimes we get our chess analysis cluttered during the game, and find we are going over the same analysis over and over. I am sure we all done this. This book helps in teaching one how to think better during the game (i.e. organize our thought process).
You also need to learn good chess openings. Learn few lines well. No need to learn very many lines. Just make sure to get to middle game in at least equal position where one then is out of the book.   Need also to learn basic end game techniques. I studied many books on end game. Rook ending, Pawn endings, and learn the basic basic patterns that can show up in end game.
But for me, the best way to get better in chess, was to go over the classic books written by the best players and read their own analysis of their games.
Fischer's my best 60 games, and Alekhine 3 book collection of "My Best Games of Chess" written by him, and "My Best Games" By Kaprov, are such examples.
This can be very time consuming also. So pick one player whose style you like, and try to study their games and do the analysis.
A good collection with good analysis is the the chess informator books. I have large collection of these books. Study the games of the players you like their styles from these books.
At the end of the day, nothing beats playing chess with player who are stronger than you. After the game, go over it and see what mistakes you did. This is how you learn also.
My best US rating was 2430 I think or around there, and my ELO is 2310 (FM). I stopped going after the IM title as I got burned from chess. I do not play active chess any more.
Just some thoughts. Hope they help.

Personally I suggest you My System by Aaron Nimzowitsch.
It is an old book but I think still valid and a must have for every chess player.


text:
Looking for a historic chess game
I'm looking for an historic chess game, and I don't remember if Capablanca or Kasparov played it. In it, both queens are face to face and neither let pass the other one, for almost 7 or 10 movements, in the middle of the board. I remember saw it on chessgames.com in 2005.
The queens moved horizontally, 1 or 2 spots. One was in the above row and the second one in the bottom, for e.g. the black queen in the 5th row and the white queen in the 4th row. So neither can't go forward, as they are blocking each other. I'm not sure if it was Capablanca or Kasparov, only about 70% sure.

Are you sure about either Capablanca or Kasparov?

Can you elaborate what you mean by "queens are face to face" and "neither let pass the other one"?

Can you elaborate more on the meaning of "neither let pass the other one"? Does it mean that the queens move away from the other queen's attack, to avoid an exchange?

Are you sure it's an actual game and not a composition? https://i.stack.imgur.com/hDsNd.png

If you know python, there might be a way to use a chess library and brute force through all games in a database like TWIC. Then represent a board and play the moves on it, stopping when the queens are blocking each other in the centre, and if one of the opponents are Kasparov or Capablanca (or some other elite player).

@Leandro yes, is on the middle of the board with more pieces

I extracted 3166 games by Capablanca or Kasparov and examined all of those in which a black Queen on the fifth rank was opposite a white Queen on the fourth rank. None of those games exhibited the characteristics described. Possibly either the player or the ranks have been mis-remembered.

You could use Python and code it to sift through Capablanca or Kasparov games. When there is a position where the queens oppose in the center, make the program put it to the side. Then, you can look through the games until you find the one you want.
If you don't know how to use Python, you could get someone else to help you, or to get a program with the same function from online.

Note that you need to download the Python software before you can run the programs.

Chess Query Language is a tool you can use to search for games like these in your database of games of choice. It shouldn't be too hard to do this- certainly easier than the (good!) suggestion of Python by others


text:
The Bishop's gambit variation of the King's gambit
I've been investigating the theory of the King's gambit, and I found the variation in the accepted 3. Nf3 Be7. I didn't like the looks of that for White.
I've started to play the Bishop's gambit, but the problem is that Black can also play the 3... Be7 line. Is there any way to deal with it?

How would you deal with it in the Nf3 Be7 line? There are several options

I would play Bc4 and after the check, Kf1, but after taking the bishop with my knight, there is no way to get rid of Black's queen.

After 1.e4 e5 2.f4 exf4 3.Bc4 Be7 4.Nf3 Bh4+ probably 5.g3!? fxg3 6.0-0 does the job.
[fen ""]

1.e4 e5 2.f4 exf4 3.Bc4 Be7 4.Nf3 Bh4+ 5.g3!? fxg3 6.O-O

In typical King's gambit style, you're down in material and probably a bit worse with perfect play, but you have great compensation and attacking chances. If Black makes a mistake, they will pay the consequences.

[fen ""]
1. e4 e5 2. f4 exf4 3. Nf3 Be7 4. Nc3! {Provoking Black to displace our king} Bh4+ (4...Nf6 {is actually the most critical try, preparing d5} 5. d4 d5 6. exd5 Nxd5 7. Bc4 Be6 (7...Bh4+ 8. g3 fxg3 9. Qe2+ Be6 10. hxg3 Bxg3+ 11. Kd1 {Opening the kingside like this gives White a lot of play as Black will castle there or leave his king in the center... just look at h7}) 8. Bxd5 Bxd5 9. Bxf4) 5. Ke2 {Looks like we are playing with fire, but is sound and also gives Black opportunity to become overzealous and make mistakes} d5 {Opening the center is probably most critical} (5...c6 6. d4 d5 7.Bxf4 dxe4 8.Nxe4 Qe7 9.Be5 f6 10.Nd6+ Kd8 11.Nxh4 fxe5 12. Ndf5 Bxf5 13. Nxf5 Qe6 14. Ne3 {check complications with engine if something is unclear}) (5...Be7 6. d4 g5 7. Qd3 {Making room for the king who will go to d1} d6 8. Kd1) (5...d6 6. d4 Bg4 7. Bxf4) 6. Nxd5 Nf6 7. Nxf6+ Qxf6 8. d3 (8. d4!? {Is more active but also risky}) Bg4 9. Qd2 Qb6 10. Kd1 Bg5 11. Be2 {Is dynamically equal. Note that this was almost perfect play by Black}

Bc4 has bigger problems than ...Be7, namely 3...Nf6 (GM Shaw even goes as far as to call it a soft refutation, i.e. Black is better in all variants). Here is what I like to play in the Nf3 variation after Be7. You might think it looks like White will go down in flames, but actually most Black players overstep heavily very fast and you get very good play.


text:
Getting wrong results in perft stats with checks and mates
The perft count works well after testing with many positions from epd files from the web
Now I want to see some perft stats like this one: https://www.chessprogramming.org/Perft_Results, from the initial position
But I'm getting bad results for checks and mates, in the wiki says in the initial position in the depth 4 there are 8 mates but I get that result in the depth 5, same for the the depth 5 in the wiki says 347 but I get that in the depth 6 and it should be 10828, what I'm doing wrong?
Here is the program output with perft to depth 6: https://pastebin.com/3DSVn9UZ
Here is the code:
typedef struct perft_stats_s {
    uint64_t captures;
    uint64_t en_passant;
    uint64_t castles;
    uint64_t promotions;
    uint64_t checks;
    uint64_t discovery_checks;
    uint64_t double_checks;
    uint64_t checkmates;
} perft_stats_s;

typedef struct perft_data_s {
    perft_stats_s stats[1];
    uint64_t nodes;
    uint64_t elapsed;
} perft_data_s;

void UpdateStats(move_t move, bool is_capture, bool in_check, board_s *board, perft_stats_s *stats)
{
    if (in_check)
    {
        uint64_t checks = attacksToKing(board);
        if (popCount(checks) == 1) {
            ++stats->checks;
            uint64_t to_sq = bb_sq(TO_SQ(move));
            if (to_sq != checks) {
                ++stats->discovery_checks;
            }
        }
        else {
            ++stats->double_checks;
        }
    }

    if (is_capture)
        ++stats->captures;
    if (MoveType(move) == MT_EP_CAPTURE) {
        ++stats->en_passant;
        ++stats->captures;
    }
    if (MoveType(move) == MT_CASTLE)
        ++stats->castles;
    if (MoveType(move) >= QUEEN_PROMOTE)
        ++stats->promotions;
}

uint64_t PerftStats(uint8_t depth, bool in_check, board_s *board, perft_stats_s *stats) {

    ASSERT(checkBoard(board));

    move_t list[MAX_MOVES];
    uint8_t count;

    if (in_check)
    {
        move_t *first = list;
        move_t *end = generateEvasion(board, list);
        count = end - first;
    }
    else
    {
        count = generateAllMoves(board, list);
    }

    uint64_t nodes = 0;
    uint8_t m;
    move_t move;
    bool is_capture;

    if (depth == 1)
    {
        for (m = 0; m < count; ++m)
        {
            move = list[m];
            is_capture = board->pieces[TO_SQ(move)] != EMPTY;
            if (!makeMove(board, move))  {
                continue;
            }
            bool inCheck = isInCheck(board);
            UpdateStats(move, is_capture, inCheck, board, stats);
            ++nodes;
            unmakeMove(board);
        }
        return nodes;
    }

    for (m = 0; m < count; ++m)
    {
        move = list[m];
        is_capture = board->pieces[TO_SQ(move)] != EMPTY;
        if (!makeMove(board, move))  {
            continue;
        }
        bool inCheck = isInCheck(board);
        uint64_t new_nodes = PerftStats(depth - 1, inCheck, board, stats);
        UpdateStats(move, is_capture, inCheck, board, stats);
        if (inCheck && new_nodes == 0) {
            ++stats->checkmates;
        } else
            nodes += new_nodes;
        unmakeMove(board);
    }
    return nodes;
}

void PerftStatsRoot(uint8_t depth, board_s *board)
{
    perft_data_s data[MAX_DEPTH];
    memset(data, 0, sizeof(perft_data_s) * MAX_DEPTH);

    perft_stats_s stats[1];
    memset(stats, 0, sizeof(perft_stats_s) * 1);

    uint64_t start = getTime();

    printf("\n");
    printf(" depth                 nodes    elapsed ms\n");

    uint64_t totalNodes = 0;
    uint8_t d;

    bool in_check = isInCheck(board);

    //for (d = 1; d <= depth; d++)
    for (d = depth; d > 0; --d)
    {
        uint64_t sp = getTime();
        uint64_t nodes = PerftStats(d, in_check, board, stats);
        totalNodes += nodes;

        memcpy(data[d].stats, stats, sizeof(perft_stats_s) * 1);
        data[d].nodes = nodes;
        data[d].elapsed = getTime() - sp;

        memset(stats, 0, sizeof(perft_stats_s) * 1);
    }

    for (d = depth; d > 0; --d)
    {
        perft_data_s *curr_data = &data[d];
        perft_data_s *prev_data = &data[d - 1];
        curr_data->stats->captures -= prev_data->stats->captures;
        curr_data->stats->en_passant -= prev_data->stats->en_passant;
        curr_data->stats->castles -= prev_data->stats->castles;
        curr_data->stats->promotions -= prev_data->stats->promotions;
        curr_data->stats->checks -= prev_data->stats->checks;
        curr_data->stats->discovery_checks -= prev_data->stats->discovery_checks;
        curr_data->stats->double_checks -= prev_data->stats->double_checks;
        curr_data->stats->checkmates -= prev_data->stats->checkmates;
    }

    for (d = 1; d <= depth; ++d)
    {
        perft_data_s *curr_data = &data[d];
        printf("%6d  %20s %10" PRIu64 "\n", d, formatNumber(curr_data->nodes), curr_data->elapsed);
        perft_stats_s *st = curr_data->stats;
        printf("    caps: %" PRIu64 "\n", st->captures);
        printf("    enpa: %" PRIu64 "\n", st->en_passant);
        printf("    cast: %" PRIu64 "\n", st->castles);
        printf("    prom: %" PRIu64 "\n", st->promotions);
        printf("    chec: %" PRIu64 "\n", st->checks);
        printf("    dich: %" PRIu64 "\n", st->discovery_checks);
        printf("    doch: %" PRIu64 "\n", st->double_checks);
        printf("    chmt: %" PRIu64 "\n", st->checkmates);
    }

    uint64_t elapsed = getTime() - start;
    uint64_t nps = NPS(elapsed, totalNodes);

    printf("\n");
    printf("depth       : %u\n", depth);
    printf("nodes       : %s\n", formatNumber(totalNodes));
    printf("nps         : %s\n", formatNumber(nps));
    printf("time        : %" PRIu64 "ms\n", elapsed);
}

I save the result in an array struct and after that I loop over the array to update the counters to show the correct counters, like this:
counter[depth] -= counter[depth - 1]

I'm afraid this question is about programming and should be answered in a programming site. Specifying the code is Java would have been great help too

questions about programming engines are on-topic, per https://chess.meta.stackexchange.com/q/418/9025

It doesn't look like you're counting mates at the leaves.  Your depth == 1 code is almost the same as the rest, except that counting mates is omitted.  This would explain why your mate counts lag behind as you described.
My suggestion would be to get rid of the depth == 1 block entirely (since to make it correct would require it to be exactly the same as the code immediately below it) and instead add a if(depth <= 0) return 1 at the top of PerftStats

I just found a mistake, in the UpdateStats the checks should be incremented after the if (in_check) now is showing the correct stats count except that mates are in the wrong depth, I guess I have to update manually, here I see that the last depth 6 the check and mate are ommited


text:
Benoni Defence Theory and Ideas
I have played the Benoni for a while, and I frequently play bad moves in the opening. How could I play the Benoni - Pawn Storm Variation safely?

What's the "pawn storm variation"?

Where White play e2-e4 and f2-f4.

I don't think it's very helpful to try and play the Benoni of all openings in a safe manner. It's an inherenly risky opening that will lead black to very bad positions if played without a willingness to play risky chess.

the Modern Benoni "is definitely not an opening for cowards." - GM Lev Psakhis

Not answering because I have no idea about the Benoni but pawn pushes tend to be bad because they weaken all squares behind them. There is a nice outpost on d4 eventually and your dark bishop has great potential. Also many have mentioned this but this variation looks to be about unbalances(like the KID or Sicilian) so if you want safe play, this isn't the best opening for you.

You shouldn't give a fig about "variations". Players don't lose games in the opening because they're bad at this variation or that system, they lose short games because they're bad at tactics (and that's your experience, yeah?).
Forget the dumb names of things. Pawn Storm This, Big Attack That. You have to learn enough tactics first.


text:
About solving Atomic Chess
Is it possible to weakly solve Atomic Chess as a win for White? I've analysed a few lines good for White, but I am not sure about a general solution.

As a decently strong atomic player fairly connected with the atomic community including the strongest players, I feel I can answer this one. The short answer is: white probably wins, but there is no weak solution nor does it currently seem achievable to find one.

Outcome?
The current consensus among the strongest players and opening theoreticians is that White wins, but as of yet there is no public and/or convincing and exhaustive proof. Opinions differ on whether many different openings and lines are winning or drawn; however there tends to be agreement that the lines after 1. Nf3 f6 2. Nc3 Nh6 3. g4 (the first tabiyas in this rabbit hole would be after 3...c6 4. d4 e6 5. e4 f5 6. Nh4 or exf5 with many sideline branches on black's 2nd, 4th and 5th moves) give no hope for black if white plays perfectly (and by "perfectly", that tends to be 20+ move deep, widely branching theory in complicated middlegames, leading to nontrivial endgames). That said, from a practical point of view, these are also not easy to meet as black at high levels.
This, however, does not constitute a weak solution. We do not have an exhaustive (or even very aggressively pruned) game tree that leads to white wins everywhere. All we have is a lot of opening theory where both sides play sensible moves and where with precise play by white, just about everything leads to what seem to be winning white endgames. The branching factor for plausible moves appears to be too high for a weak solution to be within reach, though -- in addition, the endpoint endgames themselves may not be easy to evaluate for humans, and not for engines either.

A word on engines
The modern engine for atomic analysis is Stockfish 9, but using the 2018 or earlier builds, as more recent builds seem to give pruning issues leading to outright blunders and misevaluations in certain cases. Other engines exist like Atomkraft (an older engine), and offer different but also strong opinions.
A major shortfall of atomic engines in general, though, is their endgame knowledge is poor. One commonly-occurring situation is a pawn endgame where one side is up a whole bishop, yet cannot win because the bishop cannot take an enemy pawn, nor can passed pawns be created. This is known as "pawnitisation" (common enough to have a name since more than a decade ago!) and engines cannot detect this reliably, often giving a +3 to +4 evaluation to draws. They also, due to the horizon effect, tend to misevaluate simple endgames where one side is up two pawns for minor (yes, up) with rooks on the board, which is winning in general but can take many moves.
While 6-man tablebases exist for atomic, these do not solve the problem; many of these endgames have more than six units on the board.
This leads to the issue that engines, despite being stronger than humans (still not completely invincible though!), may not be fully relied on to accurately evaluate a position.

Conclusion
An engine-only "solution" of atomic would be met by skepticism due to their inability to accurately judge a fair number of endgames. In fact, even an engine-assisted weak solution would seem unattainable, also because of the high branching factor of plausible moves, and high depths (think at least 40+, probably more than 60+) needed for reliability.

I know there is at least some degree of theory in Atomic Chess, which indicates it hasn't been solved. Also from this Wikipedia article:
https://en.wikipedia.org/wiki/Atomic_chess
Under the "Strategy" section, it says "no attempts to prove a win for White have been successful". Although the article notes that White's advantage is much larger in Atomic Chess than regular chess, which obviously makes sense.
There's a version of Stockfish out there that can play Atomic Chess. I doubt it's as strong in the game as regular Stockfish is in chess, but it shows that even with strong tools available the game seems to have not been solved.
I don't know whether it's possible to solve it in the future though. It's highly unlikely regular chess will ever be fully solved, due to the sheer complexity of the game tree. For Atomic Chess though, maybe it's possible that there's some forced win (or forced draw?) relatively early on. This could be due to a few reasons:

As noted already, White has a larger advantage in Atomic Chess.

Pieces tend to come off the board faster, due to the explosions when a piece captures. This reduces the branching factor (i.e., number of possible moves), which reduces the complexity of how many paths need to be considered in the game tree. It also simplifies the game, potentially bringing it closer to some theoretically drawn endgame (in atomic chess).

While strong, I'm not sure how good this version of Stockfish actually is in Atomic Chess, since it was developed for standard chess. Our current engines could have to get stronger in the variant before finding a hidden solution.


text:
A little chess joke
I've been studying the Bird's opening, and I wonder if I could launch a surprise with this line

f4 d5 2. Kf2?!
I can artificially castle, and I can develop naturally. Is this move playable, or just plain bad?

By the way, since the bird is fairly rare, playing 1.f4 already gives you a small amount of surprise value. Although it's debatable how much this is worth, since someone with a good opening repertoire would be reasonably prepared against it anyway.

It may be playable, but... Why? What could possibly be better about 2.Kf2 than 2.b3 or 2.Nf3? In the best case scenario, you'll en dup in a regular Bird position but several tempi down

This move is bad, however, depending on your opponent it has merit. If your opponent is 2100 and above with an understanding of how to break open a position and kill a king then it won't end well for you. On the other hand, if your intention is to provoke your opponent to attack you and then counter-attack when an opening is created it may well be okay. You must have some idea of the attacking patterns against your king and how to protect your king in those circumstances.
I wouldn't play this opening personally unless for fun and to improve my overall play -- not necessarily results. I still see some merit if you are targeting an opponent who is not a great attacker or prefers not to attack early or at all. There are some opponents who always play consolidating or slow moves in the middle of an attack which gives away the advantage. These types of opponents would be a lamb to the slaughter since you are forcing them to do something they would prefer not to do.
This is a more psychological ploy that will work against certain opponents. Of course, it goes without saying that you will have to play well since you are playing from behind. Play like a tiger and take advantage of every blink by your prey. Stalk (develop), stalk (secure king), stalk (arrange pieces to pounce), stalk (wait for a mistake -- blink), pounce.

The opponent doesn't have to be close to 2100+ for this to end badly for White, at least in a non-blitz game. If this was bullet however then I agree more with your answer - the move could potentially even work at 2300+ (since you're egging your opponent on when they barely have any time to think), depending on how skilled White is.

It's a bad move. Sure it would be surprising, but a surprising move is only effective if it's challenging for your opponent to play against (here that's reversed). The only value would be playing this as a joke in a fun game with a friend or something.
Stockfish 11 at depth 31 gives -1.48 after Black pushes 2...e5.

I'd focus more on the evaluation after a more "normal" move. After all, if Black has to play very accurately to exploit our mistake, then it probabbly has some surprise value!

@David The position after 2...Nf6 gives -1.06 at depth 30. I wouldn't call finding 2...e5 very accurate, as it's a fairly principled reaction to 2.Kf2.

Not many players would go for ...e5 there, since it's taking an unnecessary risk while 2...Nf6 gives Black an awesome position without the need to be temporarely down on material

The most important question here is: why? There is no benefit in castling artificially at this stage. There are two reasons people do that:

the rook is needed on the a/h file
they are forced to.

Neither of these apply in this situation. So artificial castling is not a good reason. Then two options remain: is the king safer on f2 or is the king providing assistance to an attack? Obviously the answer to both questions is no.
It does not matter what the level of your opponent is. There is never any benefit in playing a move that is bad regardless of the response.
The only valid reason is psychological and therefore most appropriate in blitz games: many opponents will feel a strong urge to destroy your position and might very well make some fatal mistakes in doing so. Having the initiative can be a curse, especially in blitz games.