Mahjong is a matching game that uses a set of Mahjong tiles. The 144 tiles are arranged
in special layouts with their faces upwards. A tile that can be moved left or right without disturbing other
tiles is said to be exposed. Exposed pairs of identical tiles (Flower and Seasons tiles in the same group
being considered identical) are removed from the layout one at a time, gradually exposing the lower layers
to play. The aim of the game is to clear the layout by pairing up all the tiles. The game is finished when
either the layout is empty, or there are no exposed pairs remaining.