A version of the game of Nim, as played in the film "Last Year at Marienbad." You and the computer take turns removing as many cards as you like from one row at a time; the player who takes the last card loses.
Try to figure out how the number b depends on the number a. To do this, move the point a on the real line (click and drag the blue ball) and try to identify what happens with the point b. Grades 7, Algebra I