Vol. 15 No. 6, © The Author, 2005. Published by Oxford University Press. All rights reserved.
Original Articles |
Completeness and Cut-elimination in the Intuitionistic Theory of Types
1 1615 Commonwealth Ave # 18, Brighton, MA 02135, USA. Email: mcdemarco{at}gmail.com, 2 Dept. of Math and Computer Science, Wesleyan University, Middletown, CT 06457, USA, and Visiting Researcher, Facultad de Informática, Universidad Politécnica de Madrid, Spain. Email: jlipton{at}wesleyan.edu
In this paper we define a model theory and give a semantic proof of cut-elimination for ICTT, an intuitionistic formulation of Church's theory of types defined by Miller et al. and the basis for the
Prolog programming language. Our approach, extending techniques of Takahashi and Andrews and tableaux machinery of Fitting, Smullyan, Nerode and Shore, is to prove a completeness theorem for the cut-free fragment and show semantically that cut is a derived rule. This allows us to generalize a result of Takahashi and Schütte on extending partial truth valuations in impredicative systems. We extend Andrews' notion of Hintikka sets to intuitionistic higher-order logic in a way that also defines tableau-provability for intuitionistic type theory. In addition to giving a completeness theorem without using cut we then show, using cut, how to establish completeness of more conventional term models. These models give a declarative semantics for the logic underlying the
Prolog programming language.
Keywords: Mathematical logic, type theory, lambda calculus, theorem proving, logic programming, proof theory, cut-elimination, impredicative formal systems
Received 27 April 2004.