Given an initial configuration of 8 numbered tiles on a 3 x 3 board, move the tiles in such a way so as to produce a desired goal configuration of the tiles. At each step, one tile is slid into the blank.

State = 3 x 3 array configuration of the tiles on the board.

Operators: Move Blank square Left, Right, Up or Down. (Note: this is a more efficient encoding of the operators than one in which each of four possible moves for each of the 8 distinct tiles is used.)

Initial State: A particular configuration of the board.

Goal: A particular configuration of the board.