Formalizing the Halting Problem in a Constructive Type Theory

  • Authors:
  • Kristofer Johannisson

  • Affiliations:
  • -

  • Venue:
  • TYPES '00 Selected papers from the International Workshop on Types for Proofs and Programs
  • Year:
  • 2000

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Abstract

We present a formalization of the halting problem in Agda, a language based on Martin-L枚f's intuitionistic type theory. The key features are: - We give a constructive proof of the halting problem. The "constructive halting problem" is a natural reformulation of the classic variant. - A new abstract model of computation is introduced, in type theory. - The undecidability of the halting problem is proved via a theorem similar to Rice's theorem. The central idea of the formalization is to abstract from the details of specific models of computation. This is accomplished by formulating a number of axioms which describe an abstract model of computation, and proving that the halting problem is undecidable in any model described by these axioms.