One of the very first facts that every chess player learns is that two lone Knights can not force mate. This stems from the fact that, while maneuvering the defending King into a corner, the Knights must stalemate the opponent in the process.

However, one of the ironies which makes Chess so addictive, is that the addition of an extra Pawn by the defending side often (not always) permits the Knights to win by eliminating the stalemate possibilities.

I first decided to undertake study of this endgame in 1980, while reviewing Botvinnik's analysis to the game Smyslov vs Lilienthal, 1941 . Lilienthal failed to find the path to victory, but, remarkably, he had this endgame several years earlier and also failed to win: G M Norman vs Lilienthal, 1934 .

The usual strategy is this: one Knight blockades the Pawn, while the King and the free Knight force the defending King into an unfavorable corner. The blockading Knight moves only when delivering the final execution, often allowing the Pawn to Queen.

A typical winning position is the following:

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White to play. The only choice for him to make is whether he wants to get mated on h1 or h8.

The h1 option: 1.Kg1 Kg3 2.Kf1 Kf3 3.Kg1 Nf4 4.Kh2 Kf2 5.Kh1 Kg3 6.Kg1 Ng2 7.Kf1 Kf3 8.Kg1 Ne3 9.Kh2 Kg4 10.Kg1 Kg3 11.Kh1 Kf2 12.Kh2 Ng5! 13.h7 Ng4+ 14.Kh1 Ne4 (No stalemate!) 15.h8=Q Ng3#

The h8 option: 1.Kh3 Kf3 2.Kh4 Ne5 3.Kh3 Kf2 4.Kh4 Kg2 5.Kh5 Kf3 6.Kh4 Nf7 7.Kh3 Nfg5+ 8.Kh4 Kf4 9.Kh5 Kg3 10.Kg6 Kg4 11.Kg7 Kf5 12.Kg8 Kf6 13.Kh8 Ne6! 14.Kg8 Ke7! 15.Kh8 Kf8! 16.Kxh7 Kf7 17.Kh8 Nf8 18.h7 Ng6#

There is no win if the pawn is too far advanced, obviously. Furthermore, there are also positions which require over 50 moves for mate to be forced.

For those who want to explore this endgame in more depth, I recommend Shredder Tablebase: http://www.shredderchess.com/online... .

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