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Explicit Provability And Constructive Semantics
 Bulletin of Symbolic Logic
, 2001
"... In 1933 G odel introduced a calculus of provability (also known as modal logic S4) and left open the question of its exact intended semantics. In this paper we give a solution to this problem. We find the logic LP of propositions and proofs and show that G odel's provability calculus is noth ..."
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In 1933 G odel introduced a calculus of provability (also known as modal logic S4) and left open the question of its exact intended semantics. In this paper we give a solution to this problem. We find the logic LP of propositions and proofs and show that G odel's provability calculus is nothing but the forgetful projection of LP. This also achieves G odel's objective of defining intuitionistic propositional logic Int via classical proofs and provides a BrouwerHeytingKolmogorov style provability semantics for Int which resisted formalization since the early 1930s. LP may be regarded as a unified underlying structure for intuitionistic, modal logics, typed combinatory logic and #calculus.
An intuitionistic theory of types
"... An earlier, not yet conclusive, attempt at formulating a theory of this kind was made by Scott 1970. Also related, although less closely, are the type and logic free theories of constructions of Kreisel 1962 and 1965 and Goodman 1970. In its first version, the present theory was based on the strongl ..."
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An earlier, not yet conclusive, attempt at formulating a theory of this kind was made by Scott 1970. Also related, although less closely, are the type and logic free theories of constructions of Kreisel 1962 and 1965 and Goodman 1970. In its first version, the present theory was based on the strongly impredicative axiom that there is a type of all types whatsoever, which is at the same time a type and an object of that type. This axiom had to be abandoned, however, after it was shown to lead to a contradiction by Jean Yves Girard. I am very grateful to him for showing me his paradox. The change that it necessitated is so drastic that my theory no longer contains intuitionistic simple type theory as it originally did. Instead, its proof theoretic strength should be close to that of predicative analysis.
Gödel's Dialectica interpretation and its twoway stretch
 in Computational Logic and Proof Theory (G. Gottlob et al eds.), Lecture Notes in Computer Science 713
, 1997
"... this article has appeared in Computational Logic and Proof Theory (Proc. 3 ..."
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this article has appeared in Computational Logic and Proof Theory (Proc. 3
Constructive notions of set Part I Sets in Martin–Löf type theory
"... This is the first of two articles dedicated to the notion of constructive set. In them we attempt a comparison between two different notions of set which occur in the context of the foundations for constructive mathematics. We also put them under perspective by stressing analogies and differences ..."
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This is the first of two articles dedicated to the notion of constructive set. In them we attempt a comparison between two different notions of set which occur in the context of the foundations for constructive mathematics. We also put them under perspective by stressing analogies and differences with the notion of set as codified in the classical theory Zermelo–Fraenkel. In the current article we illustrate in some detail the notion of set as expressed in Martin–Löf type theory and present the essential characters of this theory. In a second article we shall explore a distinct notion of set, as arising in the context of intuitionistic versions of Zermelo–Fraenkel set theory. The theory we shall analyse there is Aczel’s CZF (Constructive Zermelo– Fraenkel) and we shall supplement its exposition by a succinct account of Aczel’s interpretation of CZF in type theory. This will enable us to compare the two notions in a more precise sense. 1.
Russian Math. Surveys 59:2 203–229 c○2004 RAS(DoM) and LMS Uspekhi Mat. Nauk 59:2 9–36 DOI 10.1070/RM2004v059n02ABEH000715 Kolmogorov and Gödel’s approach to
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GijRAN SUNDHOLM CONSTRUCTIONS, PROOFS AND THE MEANING OF LOGICAL CONSTANTS*
"... There are cases where we mix two or more exact concepts in one intuitive concept and then we seem to arrive at paradoxical results. Hao Wang. During the last decade both mathematicians and philosophers have been interested in the development of various theories of constructions. The study of these t ..."
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There are cases where we mix two or more exact concepts in one intuitive concept and then we seem to arrive at paradoxical results. Hao Wang. During the last decade both mathematicians and philosophers have been interested in the development of various theories of constructions. The study of these theories has been prompted by at least three sorts of considerations. The first theories were proposed by Kreisel around 1960 as a means of formalizing the intended interpreation for the intuitionistic logical constants as presented in Heyting’s Introduction from 1956. Here, in Kreisel’s version, the relation construction c proves proposition A was given a stepwise analysis according to the complexity of A, in much the same way as the truthtables provide such an analysis in the classical case.