Date of Original Version



Technical Report

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Abstract or Description

Abstract: "In higher-order automated theorem proving the extensionality of equality has not yet been satisfactorily dealt with. This situation is especially unsatisfying since higher-order logic without extensionality does not admit a natural set-theoretic semantics. In this paper we present a version of Smullyan's Unifying Principle for simple type theory with extensionality. This result can serve as a tool for the development of extensionally complete calculi that are well-suited for mechanization on computers, and furthermore enables us to give an elegant completeness proof for Henkin's original calculus."