He had heard somewhere, though, that, mathematically speaking, the game of Go was more difficult than chess, in the sense that the tree of possible moves and countermoves was much vaster: far too vast even for a supercomputer to work through all the possibilities. Computer chess programs had been written that could challenge a Kasparov, but no computer program could give a high-level Go player a game that was even moderately challenging. Supposedly you couldn’t even think about Go as a logical series of specific moves and countermoves; you had to think visually, recognizing patterns and developing intuitions.