Two Knights against a Pawn.

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A nice diagram that helps to understand a quite difficult ending.

It is quite well known that two Knights cannot defeat a bare King. It would be possible, should the weak side play terribly (there are mate positions indeed, but they are always avoidable).

All of this may change if the weak side has a single pawn. Then, the strong side (in our diagram, the White) can force a stalemate position with one Knight plus the King and then, ride the other Knight to the checkmate while the weak side moves its sad pawn.

I find it difficult to force the opposite King into the corner with only one Knight and the eventual support of the other, but it can be done. It has been studied by Cheron and others.

The green squares are the ones in which the pawn can be placed so that the ending can be won.

I took the picture somewhere in the Chessbase page. The original url is not available anymore.