6

Tim Krabbe gives this position on his list of serious promotions to rook and bishop:

[FEN "8/8/5b2/8/K7/4N3/kp6/8 w - - 0 1"]
[White "Boniface"]
[Black "Pugh"]
[Site "Bristol"]
[Date "1995"]

1. Nd1 b1=B

And states that: "Although the position was then technically won for Black, he did not manage to win, and a draw was agreed at move 92."

Can black win the resulting 2 bishops vs knight ending, and if so can it be done within 50 moves to avoid a draw? I had Stockfish 5 grind at it for almost two hours and a depth of 83 but it couldn't find a win.

6

Try Syzygy tablebase: https://syzygy-tables.info/?fen=8/8/5b2/8/K7/8/k7/1b1N4_w_-_-_0_1

enter image description here

Please ignore DTZ if you don't know what it is, look at DTM. It's checkmate in 139 piles with perfect play.

No, the position is drawn under the FIDE 50-move rule.

  • 4
    The 139 and other lengths are given in plies, not in moves. (Checked with Nalimov EGTB.) Kb4 loses in 70 moves. – Rosie F Jan 28 '17 at 16:59
  • But how to know that a capture of the knight doesn't occur on move 50? – RemcoGerlich Mar 25 '17 at 14:02
  • Drawn with perfect play. That's as hard to achieve for the Knight side as it is for the Bishops. Keep playing. – Noam D. Elkies Mar 25 '17 at 15:44
2

I would suggest running Tablebase on the position - the program can calculate exactly how many moves until the end, provided there are six or less pieces.

In practical play, it is one of those endgames that borders on the brink between a draw and a win. It should be a draw with constant perfect play, but in practice it is much easier to win with the 2 B's than draw with in the one Knight.

I think even Karpov failed to draw this endgame in a game he had with Kasparov, and he was renowned for his incredible technique.

  • 1
    I think the attack is harder than defense in BB vs. N endgame, the winning process is quite irrational, I would say almost random for human understanding. I gave up on learning that endgame, just knowing some basic concepts and positions. I would bet that majority of GMs wouldn't win this endgame against human + tablebase even in 200 moves. While learning, defensive resources were much more obvious for me than long bishop moves saving 15 halfmoves for some hidden reason. Q vs. R is much easier on the attack side on the other hand. – hoacin Mar 25 '17 at 9:47
1

http://www.thechessworld.com/resources/nalimov-endgame-tables

Per Nalimov Endgme Tablebases the endgame of K+2B vs. K+N is a force win for the 2Bs in a maximum of 67 moves.

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