Some Remarks on Boolean Constraint Propagation

We study here the well-known propagation rules for Boolean constraints. First we propose a simple notion of completeness for sets of such rules and establish a completeness result. Then we show an equivalence in an appropriate sense between Boolean constraint propagation and unit propagation, a form of resolution for propositional logic. Subsequently we characterize one set of such rules by means of the notion of hyper-arc consistency introduced in Mohr & Masini (1988). Also, we clarify the status of a similar, though different, set of rules introduced in Simonis (1989) and more fully in Codognet & Diaz (1996).