19 August 2010

R vs. B Plus Knight Pawns

Here's an interesting position I discovered with the help of a tablebase. The diagrammed position is White to move (WTM). Only the moves 1.Be7 and 1.Bf8 hold the draw. The move 1.Bd6, for example, loses in 48 moves. With Black to move (BTM), Black wins with 1...Kc4 in 47 moves and with 1...Kc6 in 48; other moves allow a draw.

Placing the Pawn on g7 (instead of g6) is only a draw, whichever side is on move. Placing it on g5 is a win with BTM, but only a draw with WTM.

[FEN "8/8/6p1/1k6/8/B7/2r3PK/8 w - - 0 1"]

I didn't work out the complete theory of the resulting positions, but Black eventually ends up winning the White Pawn with the Rook, where it is in front of its own Pawn. In the drawn games, White has a neat trick that prevents the Rook from escaping its poor position without losing its own Pawn. In the won games, White is unable to set up the trick.

It turns out that Rook vs. Bishop, with both sides having Pawns on the g-file (or b-file) is known to be tricky. The side with the Bishop can aim for these positions in search of a theoretical draw.

No comments: