Canonical Pseudo-Correspondence
Yde Venema
Abstract:
Generalizing an example from Fine and inspired by a theorem in Jonsson, we
prove that any modal formula of the form \pi(p \or q) \iff \pi(p) \or \pi(q)
(with \pi(p) a positive formula) is canonical. We also prove that any such
formula is strongly sound and complete with respect to an elementary class
of frames, definable by a first order formula which can be read off from \pi.