Polgar Error
I was going over some of the basic endgames from L. Polgar's Chess: 5334 Problems, Combinations, and Games. The book's analysis for Position #5113 is incorrect: Black surprisingly can draw!
The provided solution is 1.e8=Q, followed by 1...e1=Q(?) 2.Kf6+ and White wins.
However, Black has a surprising draw if instead they play 1...Ke3!:
At this point, I'd like to quote from Muller and Lamprecht's Fundamental Chess Endings: "If {a single pawn} has advanced to the seventh rank and is threatening to promote, everything depends on whether the attacking king can assist the queen. With a central pawn, this is almost always possible, no matter how far away the king is." I briefly touched on these endgames in this earlier post.
Here we have an exception to this "almost always" rule. It turns out that White has an unfortunate placement of king and queen. For example, 2.Kf5+ Kf2!
Black's king hides in the shadow of White's, and supports the pawn's promotion. The queen lacks any move that prevents Black from obtaining their own queen (e.g. by delivering check or by pinning the pawn to the king).
I've been entering endgame positions for books into databases. One reason is that I can later play these positions vs. the computer and practice my endgame technique. Another reason is that I can explore variations not mentioned in the books to make sure I understand the positions thoroughly. However, here we can see one final benefit, especially if you have endgame tablebases at your disposal: you can find errors in old analysis and learn new tricks.