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DOI: 10.4230/LIPIcs.RTA.2012.133
URN: urn:nbn:de:0030-drops-34899
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Cousineau, Denis ; Hermant, Olivier

A Semantic Proof that Reducibility Candidates entail Cut Elimination

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Two main lines have been adopted to prove the cut elimination theorem:
the syntactic one, that studies the process of reducing cuts, and the
semantic one, that consists in interpreting a sequent in some algebra
and extracting from this interpretation a cut-free proof of this very

A link between those two methods was exhibited by studying in a
semantic way, syntactical tools that allow to prove (strong)
normalization of proof-terms, namely reducibility candidates. In the
case of deduction modulo, a framework combining deduction and
rewriting rules in which theories like Zermelo set theory and higher
order logic can be expressed, this is obtained by constructing a
reducibility candidates valued model. The existence of such a pre-model for a theory entails strong normalization of its
proof-terms and, by the usual syntactic argument, the cut elimination

In this paper, we strengthen this gate between syntactic and semantic
methods, by providing a full semantic proof that the existence of a
pre-model entails the cut elimination property for the considered
theory in deduction modulo. We first define a new simplified variant
of reducibility candidates à la Girard, that is sufficient to
prove weak normalization of proof-terms (and therefore the cut
elimination property). Then we build, from some model valued on the
pre-Heyting algebra of those WN reducibility candidates, a regular
model valued on a Heyting algebra on which we apply the usual
soundness/strong completeness argument.

Finally, we discuss further extensions of this new method towards
normalization by evaluation techniques that commonly use Kripke

BibTeX - Entry

  author =	{Denis Cousineau and Olivier Hermant},
  title =	{{A Semantic Proof that Reducibility Candidates entail Cut Elimination}},
  booktitle =	{23rd International Conference on Rewriting Techniques and Applications (RTA'12) },
  pages =	{133--148},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-38-5},
  ISSN =	{1868-8969},
  year =	{2012},
  volume =	{15},
  editor =	{Ashish Tiwari},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  URN =		{urn:nbn:de:0030-drops-34899},
  doi =		{10.4230/LIPIcs.RTA.2012.133},
  annote =	{Keywords: cut elimination, reducibility candidates, (pre-)Heyting algebras}

Keywords: cut elimination, reducibility candidates, (pre-)Heyting algebras
Collection: 23rd International Conference on Rewriting Techniques and Applications (RTA'12)
Issue Date: 2012
Date of publication: 29.05.2012

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