The eight puzzle is a 3x3 array containing eight square pieces, numbered 1 through 8, and one empty space. A piece can be moved horizontally or vertically into the empty space, in effect exchanging the positions of the piece and the empty space. There are four possible moves, UP (move the blank space up), DOWN, LEFT, and RIGHT.
The object of the game is to make a sequence of moves that will convert the board from the start state into the goal state:
| 1 | 3 | 4 |
| 8 | 6 | 2 |
| 7 | 5 | |
| 1 | 2 | 3 |
| 8 | 4 | |
| 7 | 6 | 5 |
This example can be solved by the operator sequence UP, RIGHT, UP, LEFT, DOWN.