433 research outputs found
Semantic A-translation and Super-consistency entail Classical Cut Elimination
We show that if a theory R defined by a rewrite system is super-consistent,
the classical sequent calculus modulo R enjoys the cut elimination property,
which was an open question. For such theories it was already known that proofs
strongly normalize in natural deduction modulo R, and that cut elimination
holds in the intuitionistic sequent calculus modulo R. We first define a
syntactic and a semantic version of Friedman's A-translation, showing that it
preserves the structure of pseudo-Heyting algebra, our semantic framework. Then
we relate the interpretation of a theory in the A-translated algebra and its
A-translation in the original algebra. This allows to show the stability of the
super-consistency criterion and the cut elimination theorem
Deduction modulo theory
This paper is a survey on Deduction modulo theor
Interactive Learning-Based Realizability for Heyting Arithmetic with EM1
We apply to the semantics of Arithmetic the idea of ``finite approximation''
used to provide computational interpretations of Herbrand's Theorem, and we
interpret classical proofs as constructive proofs (with constructive rules for
) over a suitable structure \StructureN for the language of
natural numbers and maps of G\"odel's system \SystemT. We introduce a new
Realizability semantics we call ``Interactive learning-based Realizability'',
for Heyting Arithmetic plus \EM_1 (Excluded middle axiom restricted to
formulas). Individuals of \StructureN evolve with time, and
realizers may ``interact'' with them, by influencing their evolution. We build
our semantics over Avigad's fixed point result, but the same semantics may be
defined over different constructive interpretations of classical arithmetic
(Berardi and de' Liguoro use continuations). Our notion of realizability
extends intuitionistic realizability and differs from it only in the atomic
case: we interpret atomic realizers as ``learning agents''
On the convergence of reduction-based and model-based methods in proof theory
In the recent past, the reduction-based and the model-based methods to prove
cut elimination have converged, so that they now appear just as two sides of
the same coin. This paper details some of the steps of this transformation
Virtual Evidence: A Constructive Semantics for Classical Logics
This article presents a computational semantics for classical logic using
constructive type theory. Such semantics seems impossible because classical
logic allows the Law of Excluded Middle (LEM), not accepted in constructive
logic since it does not have computational meaning. However, the apparently
oracular powers expressed in the LEM, that for any proposition P either it or
its negation, not P, is true can also be explained in terms of constructive
evidence that does not refer to "oracles for truth." Types with virtual
evidence and the constructive impossibility of negative evidence provide
sufficient semantic grounds for classical truth and have a simple computational
meaning. This idea is formalized using refinement types, a concept of
constructive type theory used since 1984 and explained here. A new axiom
creating virtual evidence fully retains the constructive meaning of the logical
operators in classical contexts.
Key Words: classical logic, constructive logic, intuitionistic logic,
propositions-as-types, constructive type theory, refinement types, double
negation translation, computational content, virtual evidenc
On completeness of reducibility candidates as a semantics of strong normalization
This paper defines a sound and complete semantic criterion, based on
reducibility candidates, for strong normalization of theories expressed in
minimal deduction modulo \`a la Curry. The use of Curry-style proof-terms
allows to build this criterion on the classic notion of pre-Heyting algebras
and makes that criterion concern all theories expressed in minimal deduction
modulo. Compared to using Church-style proof-terms, this method provides both a
simpler definition of the criterion and a simpler proof of its completeness.Comment: 24 page
On formal aspects of the epistemic approach to paraconsistency
This paper reviews the central points and presents some recent developments of the epistemic approach to paraconsistency in terms of the preservation of evidence. Two formal systems are surveyed, the basic logic of evidence (BLE) and the logic of evidence and truth (LET J ), designed to deal, respectively, with evidence and with evidence and truth. While BLE is equivalent to Nelson’s logic N4, it has been conceived for a different purpose. Adequate valuation semantics that provide decidability are given for both BLE and LET J . The meanings of the connectives of BLE and LET J , from the point of view of preservation of evidence, is explained with the aid of an inferential semantics. A formalization of the notion of evidence for BLE as proposed by M. Fitting is also reviewed here. As a novel result, the paper shows that LET J is semantically characterized through the so-called Fidel structures. Some opportunities for further research are also discussed
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