Hackenbush is played on an image consisting of line segments (either red, blue, or green) where there is a path from each line segment to the ground (a horizontal line at the bottom of the picture). Each line segment is connected to either the ground or other line segments at the endpoints. Each of the two players is assigned a color (either red or blue). On their turn, a player removes one line segment of their color (or a green line segment) and then all line segments that are no longer connected to the ground. If a player cannot make a move, she loses. Hackenbush was introduced in the 1981 book set Winning Ways for Your Mathematical Plays (by Berlekamp, Conway, and Guy), and is used as a motivating example of partizan games (that is, games in which, unlike nim, each player has moves not allowed the other player).