Wythoff's game

Wythoff's game is a two-player mathematical subtraction game played with two piles of counters. Players take turns removing counters from one or both piles, and when they remove from both piles the numbers taken from each must be equal. The player who removes the last counter or counters wins. An equivalent form places a single chess queen on a large grid, where each player moves it south, west or southwest any number of steps and the winner moves it into the corner. Martin Gardner wrote in 1977 that the game was played in China as picking stones, and the Dutch mathematician W. A. Wythoff published an analysis of it in 1907.