Rémi Coulom spent the last decade building software that can play the ancient game of Go better than practically any other machine on earth. He calls his creation Crazy Stone. Early last year, at the climax of a tournament in Tokyo, it challenged the Go grandmaster Norimoto Yoda, one of the world’s top human players, and it performed remarkably well. In what’s known as the Electric Sage Battle, Crazy Stone beat the grandmaster. But the win came with a caveat.