John H. Conway introduced this sliding tile puzzle, which bears the same relation to the Mathieu group as Sam Lloyd's famous 15 puzzle bears to the alternating group . ( was one of the first sporadic simple groups to be discovered.) Initially, tiles numbered 1–12 are placed on the same-numbered points of a projective plane of order three, with the point left uncovered. Hovering over a tile reveals the four points in the unique line of the projective plane that connects it to the uncovered point. Clicking the tile executes the sole legal move of the game, which is a double transposition: the clicked tile slides in to the uncovered space, and the other two points on the line exchange positions. The object, of course, is to restore the tiles to their initial order from a scrambled position.