Logical animation with modal logics

A specification of requirements is sometimes seen as the basis of a contract between customer and supplier. Rigorous, verifiable design and implementation is possible if the specification language is formally defined. But to produce a satisfactory, as opposed to a formally correct, system one must, amongst other things, be confident that the specification faithfully describes the real requirements. To gain this confidence the author validates the specification. In the Forest project he calls the symbolic execution process logical animation because the animator displays a logical model of the formal specification. In this case the specification presents an axiomatic theory in a modal action logic, modal because of the distinction between formulas which hold in a state, or situation, and those which will be true after some action