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).
Citation
Silvio Ghilardi. Lorenzo Sacchetti. "Filtering unification and most general unifiers in modal logic." J. Symbolic Logic 69 (3) 879 - 906, September 2004. https://doi.org/10.2178/jsl/1096901773
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