TacTix � created by the brilliantly playful Piet Hein � is basically a three-dimensional version of the old (perhaps very old) game NIM.

Like NIM, the rules of TacTix are simple. The players start with a four-by-four array of checkers and take turns removing them until the loser is forced to pick up the last piece. Players can pick up as many pieces as they like as long as they are contiguous pieces (pieces that are touching each other) in the same row or column.

Here's how a typical game might go:

The first player takes three from the second row.

The second player takes two from the second column.

The first player takes four from the fourth column.

The second player takes three from the first row.

The first player takes one from the first column.

The second player takes two from the third column forcing the first player to take the last piece and lose the game.