Anne v.d.L. Gardner

The object is to bring the situation, or problem state, forward from its initial configuration to one satisfying a goal condition. For example, an initial situation might be the placement of chessmen on the board at the beginning of the game; the desired goal, any board configuration that is a checkmate; and the operators, rules for the legal moves in chess. This difference is then used to index the (forward) operator most relevant to reducing the difference. If this especially relevant operator cannot be immediately applied to the present problem state, subgoals are set up to change the problem state so that the relevant operator can be applied. After these subgoals are solved, the relevant operator is applied and the resulting, modified situation becomes a new starting point from which to solve for the original goal.