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Proof Transformations in HigherOrder Logic
, 1987
"... We investigate the problem of translating between different styles of proof systems in higherorder logic: analytic proofs which are well suited for automated theorem proving, and nonanalytic deductions which are well suited for the mathematician. Analytic proofs are represented as expansion proofs, ..."
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We investigate the problem of translating between different styles of proof systems in higherorder logic: analytic proofs which are well suited for automated theorem proving, and nonanalytic deductions which are well suited for the mathematician. Analytic proofs are represented as expansion proofs, H, a form of the sequent calculus we define, nonanalytic proofs are represented by natural deductions. A nondeterministic translation algorithm between expansion proofs and Hdeductions is presented and its correctness is proven. We also present an algorithm for translation in the other direction and prove its correctness. A cutelimination algorithm for expansion proofs is given and its partial correctness is proven. Strong termination of this algorithm remains a conjecture for the full higherorder system, but is proven for the firstorder fragment. We extend the translations to a nonanalytic proof system which contains a primitive notion of equality, while leaving the notion of expansion proof unaltered. This is possible, since a nonextensional equality is definable in our system of type theory. Next we extend analytic and nonanalytic proof systems and the translations between them to include extensionality. Finally, we show how the methods and notions used so far apply to the problem of translating expansion proofs into natural deductions. Much care is taken to specify this translation in a
Cumulative HigherOrder Logic as a Foundation for Set Theory
"... The systems K of transnite cumulative types up to are extended to systems K 1 that include a natural innitary inference rule, the socalled limit rule. For countable a semantic completeness theorem for K 1 is proved by the method of reduction trees, and it is shown that every model of K 1 ..."
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The systems K of transnite cumulative types up to are extended to systems K 1 that include a natural innitary inference rule, the socalled limit rule. For countable a semantic completeness theorem for K 1 is proved by the method of reduction trees, and it is shown that every model of K 1 is equivalent to a cumulative hierarchy of sets. This is used to show that several axiomatic rstorder set theories can be interpreted in K 1 , for suitable . Keywords: cumulative types, innitary inference rule, logical foundations of set theory. MSC: 03B15 03B30 03E30 03F25 1 Introduction The idea of founding mathematics on a theory of types was rst proposed by Russell [20] (foreshadowed already in [19]), and subsequently implemented by Whitehead and Russell [26]. The formal systems presented in these works were later simplied and cast into their modern shape by Ramsey [18]. Godel [9] and Tarski [25] were the rst to restrict the type structure to types of unary predi...
Collections, Sets and Types
, 1995
"... We give a first order formulation of Church's type theory in which types are mere sets. This formulation is obtained by replacing λcalculus by a language of combinators (skolemized comprehension schemes), introducing a distinction between propositions and their contents, relativizing quantifiers an ..."
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We give a first order formulation of Church's type theory in which types are mere sets. This formulation is obtained by replacing λcalculus by a language of combinators (skolemized comprehension schemes), introducing a distinction between propositions and their contents, relativizing quantifiers and at last replacing typing predicates by membership to some sets. The theory obtained this way has both a type theoretical flavor and a set theoretical one. Like set theory, it is a first order theory, and it uses only one notion of collection. Like type theory, it gives an explicit notation for objects, a primitive notion of function and propositions are objects.
Completeness and CutElimination in the . . .
, 2004
"... In this paper we give a semantic proof of cutelimination for ICTT. ICTT is an intuitionistic formulation of Church's theory of types defined by Miller, Scedrov, Nadathur and Pfenning in the late 1980s. It is the basis for the *prolog programming language. Our approach, extending techniques of Taka ..."
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In this paper we give a semantic proof of cutelimination for ICTT. ICTT is an intuitionistic formulation of Church's theory of types defined by Miller, Scedrov, Nadathur and Pfenning in the late 1980s. It is the basis for the *prolog programming language. Our approach, extending techniques of Takahashi, Andrews and tableaux machinery of Fitting, Smullyan, Nerode and Shore, is to prove a completeness theorem for the cutfree fragment, and show, semantically, that cut is a derived rule. The technique used allows us to extract a generalization of the TakahashiSch"utte lemma on extending semivaluations in impredicative systems. We strengthen Andrews ' notion of Hintikka sets to intuitionistic logic in a way that also defines tableauprovability for intuitionistic type theory. We develop a corresponding model theory for ICTT and, after giving a completeness theorem without using cut we then show, using cut, how to establish completeness of more conventional term models. Our work