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ON EQUATIONAL COMPLETENESS THEOREMS
Published online by Cambridge University Press: 13 September 2021
Abstract
A logic is said to admit an equational completeness theorem when it can be interpreted into the equational consequence relative to some class of algebras. We characterize logics admitting an equational completeness theorem that are either locally tabular or have some tautology. In particular, it is shown that a protoalgebraic logic admits an equational completeness theorem precisely when it has two distinct logically equivalent formulas. While the problem of determining whether a logic admits an equational completeness theorem is shown to be decidable both for logics presented by a finite set of finite matrices and for locally tabular logics presented by a finite Hilbert calculus, it becomes undecidable for arbitrary logics presented by finite Hilbert calculi.
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- © The Author(s), 2021. Published by Cambridge University Press on behalf of The Association for Symbolic Logic
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Dedicated to Professor Ramon Jansana on the occasion of his retirement
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