Positive arithmetic without exchange is a subclassical logic

  • Authors:
  • Stefano Berardi;Makoto Tatsuta

  • Affiliations:
  • Department of Computer Science, University of Turin, Torino, Italy;National Institute of Informatics, Tokyo, Japan

  • Venue:
  • APLAS'07 Proceedings of the 5th Asian conference on Programming languages and systems
  • Year:
  • 2007

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Abstract

This paper shows the equivalence for provability between two infinitary systems with the ω-rule. One system is the positive one-sided fragment of Peano arithmetic without Exchange rules. The other system is two-sided Heyting Arithmetic plus the law of Excluded Middle for Σ10 -formulas, and it includes Exchange. Thus, the logic underlying positive Arithmetic without Exchange, a substructural logic, is shown to be a logic intermediate between Intuitionism and Classical Logic, hence a subclassical logic. As a corollary, the authors derive the equivalence for positive formulas among provability in those two systems and validity in two apparently unrelated semantics: Limit Computable Mathematics, and Game Semantics with 1-backtracking.