The Journal of Symbolic Logic

Research Article

Filtering unification and most general unifiers in modal logic

Silvio Ghilardia1 and Lorenzo Sacchettia2

a1 Dipartimento di Scienze Dell'informazione, Università Degli Studi, Via Comelico 39, 20135 Milano, Italy, E-mail: [email protected]

a2 Dipartimento di Scienze Dell'informazione, Università Degli Studi, Via Comelico 39, 20135 Milano, Italy, E-mail: [email protected]

Abstract.

We characterize (both from a syntactic and an algebraic point of view) the normal K4-logics for which unification is filtering. We also give a sufficient semantic criterion for existence of most general unifiers, covering natural extensions of K4.2+ (i.e., of the modal system obtained from K4 by adding to it, as a further axiom schemata, the modal translation of the weak excluded middle principle).

(Received July 09 2002)

(Revised April 08 2004)

Key words and phrases

  • Model logic;
  • E-unification;
  • descriptive fames;
  • projective algebras