Rybka and underpromotion ?

[M ANSARI]

Initially Rybka did not have any under-promotions at all. Joker still doesn't have them. I was surprised how often it loses a game because of an unexpected under-promotion, though. I have seen that several times now.

Actually under promotion is not so rare and happens relatively often ... at least in the sense of rare games. The time where this happens most often is that when a promotion to a knight allows a check. With a rook that might also be helpful to avoid a stalemate ... but to be honest, I have yet to see a single game where a bishop under promotion changed the outcome of the game. I am not saying it never has happened, but it is very very rare and I personally have never seen it in a real game.