Filtering unification and most general unifiers in modal logic
Silvio Ghilardi, Lorenzo Sacchetti · Journal of Symbolic Logic · 2004
Abstract. We characterize (both from a syntactic and an algebraic point of view) the normalK4-logics for which unification is filtering. We also give a sufficient semantic criterion for existence of most general unifiers, covering natural extensions ofK4.2+(i.e., of the modal system obtained fromK4 by adding to it, as a further axiom schemata, the modal translation of the weak excluded middle principle).