Statement Inversion and Strongest Postcondition

A notion of inverse commands is deened for a language with a weakest precondition semantics, permitting both demonic and angelic nondeterminism as well as miracles and nontermination. Every conjunctive and terminating command is invertible, the inverse being non-miraculous and disjunctive. A simulation relation between commands is described using inverse commands. A generalized form of inverse is deened for arbitrary conjunc-tive commands. The generalized inverses are shown to be closely related to strongest postconditions.