Varying interpolation and amalgamation in polyadic MV-algebras

Abstract

We prove several interpolation theorems for many-valued infinitary logic with quantifiers by studying expansions of MV-algebras in the spirit of polyadic and cylindric algebras. We prove for various reducts of polyadic MV-algebras of infinite dimensions that if is the free algebra in the given signature, , is in the subalgebra of generated by , is in the subalgebra of generated by and , then there exists an interpolant in the subalgebra generated by and such that . We call this a varying interpolation property because the integer depends on the inequality . We also address cases where this interpolation property fails, but other weaker (also varying) ones hold. One such interpolation theorem says that though an interpolant may not be found as above, an interpolant can always be found if finitely many universal quantifiers are applied to making it smaller and the same number of existential quantifiers are applied to making it bigger. This number of quantifiers also varies; it depends on the inequality . Several amalgamation theorems for classes (mostly varieties) of polyadic MV-algebras are obtained. Completeness theorems, relative to Hilbert-style axiomatisations, for the corresponding infinitary many-valued predicate logics are derived using the methodology of algebraic logic.