This game is played on an empty NxN square board (say 8x8):
TURNS - At each turn, each player must do the following actions:
First, drop a friendly stone on an empty cell;
Second, all pieces in the same horizontal and vertical rows move one cell nearer to the placed piece, if possible.
GOAL - If at the end of the move, there are any pieces that have an enemy piece at each diagonally adjacent cell, 4 in all, then the player with the most such pieces wins. If these numbers are equal, the game continues.