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.
8-Puzzle
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.