CRYSTALS

Copyright (c) 1970s Eric Solomon

Crystals starts on an square empty board (say, 19x19):

CRYSTAL - A crystal is a set of orthogonally connected pieces of the same color, with the following restrictions: They must be symmetric (vertical and horizontal) along the center of the crystal, i.e., each side (top, bottom, left or right) is the mirror image of the others (after rotation). The stones must be orthogonally connected. Crystals cannot have holes. DROP - On each turn, each player drops a stone on an empty cell. After the drop, the player may grow a crystal if he has at least four stones on board belonging to it, and there is no enemy stone inside. GOAL - When all cells are occupied (or when both players decide the game is over) wins the player with more stones belonging to crystals.

 

	Some valid crystals
	Some invalid crystals The top left is symmetric, but has an hole on it and the stones are not orthogonally connected. All the others are not horizontal or vertical symmetric at the center.
	Growing crystals White may grow a crystal with those four stones. White usually should choose the biggest crystal he can according to the restrictions. In this case, the crystal is defined by the green dots. Players may drop friendly stones over the crystal or just make a drawing (if playing on paper) defining the crystal. In any case, the opponent cannot drop stones inside grown crystals.