Schloss Dagstuhl - Leibniz-Zentrum für Informatik GmbH Schloss Dagstuhl - Leibniz-Zentrum für Informatik GmbH scholarly article en van Oostrom, Vincent; Toyama, Yoshihito License: Creative Commons Attribution 3.0 Unported license (CC-BY 3.0)
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URN: urn:nbn:de:0030-drops-59862


Normalisation by Random Descent



We present abstract hyper-normalisation results for strategies. These results are then applied to term rewriting systems, both first and higher-order. For example, we show hyper-normalisation of the left--outer strategy for, what we call, left--outer pattern rewrite systems, a class comprising both Combinatory Logic and the lambda-calculus but also systems with critical pairs. Our results apply to strategies that need not be deterministic but do have Newman's random descent property: all reductions to normal form have the same length, with Huet and Lévy's external strategy being an example. Technically, we base our development on supplementing the usual notion of commutation diagram with a notion of order, expressing that the measure of its right leg does not exceed that of its left leg, where measure is an abstraction of the usual notion of length. We give an exact characterisation of such global commutation diagrams, for pairs of reductions, by means of local ones, for pairs of steps, we dub Dyck diagrams.

BibTeX - Entry

  author =	{Vincent van Oostrom and Yoshihito Toyama},
  title =	{{Normalisation by Random Descent}},
  booktitle =	{1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)},
  pages =	{32:1--32:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-010-1},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{52},
  editor =	{Delia Kesner and Brigitte Pientka},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  URN =		{urn:nbn:de:0030-drops-59862},
  doi =		{10.4230/LIPIcs.FSCD.2016.32},
  annote =	{Keywords: strategy,  hyper-normalisation, commutation, random descent}

Keywords: strategy, hyper-normalisation, commutation, random descent
Seminar: 1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)
Issue date: 2016
Date of publication: 17.06.2016

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