Y (game)

Y is an abstract strategy board game, first described by John Milnor in the early 1950s.

As in most games of this type, one player takes the part of Black and one takes the part of White; they place stones on the board one at a time, neither removing nor moving any previously placed stones.

Consider a board subdivided by a line of white and black pieces into three sections.

Thus the present "official" board is essentially a geodesic dome hemisphere squashed flat into a triangle to provide this effect.

An important point is that an extra stone on the board is never a disadvantage in Y. Y is a complete and perfect information game in which no draw can be conceived, so there is a winning strategy for one player.

It is nevertheless possible for the first player to lose by making a sufficiently bad move, since although that stone has value, it may have significantly less value than the second move—an important consideration for understanding the nature of the pie rule.

It is up to the judgement of the second player to make this difficult determination and invoke the pie rule accordingly.