A Note on Chapman's Modal Truth Criterion

The formal statement of the Modal Truth Criterion presented by Chapman [1] is shown not to be necessary, in contradiction of Chapman's original claim that the criterion is both necessary and sufficient. This is achieved through the presentation of a counter-example which is a partial plan in which a goal is necessarily true, and yet fails to satisfy Chapman's criterion. A corollary of this result is that the validity checking problem for partial plans, claimed by Chapman to be polynomially solvable, is now open.

[1]  David Chapman,et al.  Planning for Conjunctive Goals , 1987, Artif. Intell..