fix(02): typos
fix(02): typos

soonhokong/lean-tutorial,fpvandoorn/tutorial,soonhokong/lean-tutorial,fpvandoorn/tutorial,Hodapp87/cs6460_project,avigad/tutorial,Hodapp87/cs6460_project,leanprover/tutorial,fpvandoorn/tutorial,leanprover/tutorial,avigad/tutorial,Hodapp87/cs6460_project,leanprover/tutorial,avigad/tutorial,soonhokong/lean-tutorial