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When a pawn reaches the end of the board, the rules say that it may be exchanged for any other piece (except a king, of course). In practice, however, promoting to anything other than a queen is very rare. Occasionally, you may have to choose a rook rather than a queen to avoid stalemate. White king on a5 and pawn on c7 against Black king on a7 is a simple case. Sometimes, you may have to choose a knight because it delivers check where a queen would not. White king on f8, pawn on g7; black king on f6, rook on a7 is a well-known example: 1.g8=Q allows mate, 1.g8=N+ lets White escape with a draw.

Such cases, however, are rare, which makes today's position, composed by VS Kovalenko in 1985, such a fine discovery. It is White to play and win and the innocuous setting with only kings and pawns hides some treats.

The first move is obvious enough: 1.d7, which leaves Black two options. The natural 1...a2 tempts White to continue 2.d8=Q a1=Q 3.Qd4+ when 3...Ka2 4.Qxa1+ Kxa1 5.c5 wins easily. But Black draws with 3...Kxb3! when 4.Qxa1 is stalemate. White's mistake was promoting to a queen. After 1.d7 a2 he should play 2.d8=B!! If the black pawn promotes, then 3.Bf6+ will win - there's no stalemate.

But what if Black plays 1...Kxb3? Then after 2.d8=Q a2, White has no queen check and any move covering the a1 square is met by 3...a1=Q leading again to stalemate. The answer is 2.d8=R! when Black's best is 2...Ka2 (2...a2 3.Ra8 Kb2 4.c5 b3 5.Kc4 wins for White) 3.c5 b3 4.c6 b2 5.Rb8 Ka1 6.c7 a2 7.Rxb2! Kxb2 8.c8=Q a1=Q 9.Qc3+ Ka2 10.Qc4+ Ka3 11.Qa6+ Kb2 12.Qb5+ Ka3 13.Qa5+ Kb2 14.Qb4+ Ka2 15.Kc2! and White wins.