The L game was invented by Edward De Bono, intended to illustrate lateral thinking.

The game violates a number of classic assumptions concerning board games, to make a board game with very few pieces that remains interesting to play.

L game starting position

The game is played on board consisting of 4×4 squares. Each player has a 3×2 L-shaped piece, and there are two 1×1 neutral pieces. On each move, a player must move first his L piece, and then may move a single neutral piece. The loser is the first player unable to move his L piece to a new position.

One basic strategy is to use a neutral piece and one's own piece to block a 3×3 square in one corner, and use a neutral piece to prevent the opponent's L piece from swapping to a mirror-image position. Another basic strategy is to move an L piece to block a half of the board, and use the neutral pieces to prevent the opponent's possible alternate positions.

These positions can often be achieved once a neutral piece is left in one of the eight killer spaces on the perimeter of the board. The killer spaces are the spaces on the perimeter, but not in a corner. On the next move, one either makes the previously placed killer a part of one's square, or uses it to block a perimeter position, and makes a square or half-board block with one's own L and a moved neutral piece.

Analysis


All possible final positions 



All positions, red to move, where red will lose to a perfect blue, and maximum number of moves remaining for red. By looking ahead one move and ensuring one never ends up in any of the above positions, one can avoid losing.

In a game with two perfect players, neither will ever win or lose. The L game is small enough to be completely solvable. There are 2296 different possible valid ways the pieces can be arranged, not counting a rotation or mirror of an arrangement as a new arrangement, and considering the two neutral pieces to be identical. Any arrangement can be reached during the game, with it being any player's turn. Each player has lost in 15 of these arrangements, if it is that player's turn. The losing arrangements involve the losing player's L-piece touching a corner. Each player will also soon lose to a perfect player in an additional 14 arrangements. A player will be able to at least force a draw (by playing forever without losing) from the remaining 2267 positions.

Even if neither player plays perfectly, defensive play can continue indefinitely if the players are too cautious to move a neutral piece to the killer positions. If both players are at this level, a sudden-death variant of the rules permits one to move both neutral pieces after moving. A player who can look three moves ahead can defeat defensive play using the standard rules.
Availability
A commercial version of the L game is made by Rex Games.

A homemade version can be made using the corner of a chessboard for the board, pawns used as neutral pieces, and stiff wire (e.g. from a clothes hanger) used to construct the L pieces and the angle to mark two sides of the board.

Trivia
The Finnish computer magazine MikroBITTI once held a competition about creating a computer version of L game. Readers could write their own computer versions of the game, on Amiga, Atari ST or PC computers, in a programming language of their own choosing, and send them in to the competition. The magazine then ranked them according to presentation, features, skill of computer opponent (if available), and general "fun factor". The winning game was written on the Amiga.