What a way to win

During during the World Championship in Mexico, the computer match Rybka-Zappa was played. In the fourth game something happened that made me lose interest in this match (and actually in computer-computer matches in general). In Chess Today issue 2530 (which came out last Friday) IM Andrey Deviatkin analysed some games of the Rybka-Zappa match and after reading this, I feel obliged to tell the ?¢‚Ǩ?ìtruth?جø¬?? about game 4.

We paid attention to this match right before it started by publishing the press conference, and now we return to it. As you probably know, the outcome was a surprising 5,5-4,5 victory by Zappa. (You can download the PGN file with the ten games here.) The main explanation for their success, given by the Zappa team, was the fact that the engines were playing on 8-core machines. "Zappa is slightly stronger than Rybka on these platforms."

It's not that I want to treat Zappa's victory with disregard ?¢‚Ǩ‚Äú beating Rybka in a match is a fine achievement ?¢‚Ǩ‚Äú but what happened in game 4 resulted in some scepticism on my part about games between computers. First I give IM Deviatkin's analysis.



The course of events was a bit different. I was standing next to the board and computers, chatting with the operators and the arbiter, while the engines were calculating their moves. Around move 100, the Rybka operator offered a draw to the Zappa team. (An interesting sidenote: if the Zappa team had agreed, the arbiter David Levy would have had to agree on the draw as well. One of his tasks is to check if the engines themselves both think it's a draw, not just the operators!)

But?¢‚Ǩ¬¶ the Zappa operator declined the draw offer! Quite surprisingly, since it had zero winning chances. (It did have a reliable fortress, as Deviatkin writes, but certainly not more than that.) The good thing is that I could ask right then and there what was going on, since engines do not have ears.

Here it comes: the Zappa operator knew that if the game would continue for a while, soon 50 moves would be played without pawn moves or captures. He knew that Rybka would then sacrifice a pawn, because the engine understands the 50-move rule and since its evalutation was higher than 0.00 (because of the material plus) sacrificing a pawn was the only way to continue the game. So by declining the draw offer, the Zappa team knew they would soon win a pawn! This remarkable strategy eventually got Zappa the full point and got me leave the playing hall in disbelief.

Epilogue: It's seems strange that the arbiter has to approve on a draw, but not on offering, accepting or declining a draw offer. One way to improve these engines even more is perhaps to program them to offer a draw themselves. But well, then such a match would be all too inhuman...