The board is a cube with four cells in each direction, with total of 64 cells.
Players take turns in putting their signs, and , in available cells.
Once a cell is used, it cannot be freed, and only one sign can be in a cell. The winner is the first player who puts four of her signs in a straight line. The line can be in any direction through the cube. However, there is no simple algorithm based on which the first player always wins. The algorithm I implement is based on a heuristic evaluation function.