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Undecidable complexity statements in -arithmetic

Published online by Cambridge University Press:  12 March 2014

Ron Sigal*
Affiliation:
Department of Computer and Information Science, Brooklyn College, Brooklyn, New York 11210
*
Dipartimento di Matematica, Università di Catania, 95125 Catania, Italy

Extract

The failure of a large and diverse body of work to settle some of the now-classical questions of computational complexity (notably P =? NP) suggests that they might not, in fact, be resolvable by established proof techniques.

Hartmanis and Hopcroft [HH] raised the issue of independent statements about computational complexity in 1976, constructing, for any consistent r.e. theory T capable of expressing statements about Turing machines, a Turing machine MT such that statements which intuitively express the computational complexity of MT are independent of T. Their technique involves a simple diagonalizing search over the theorems of T. In this paper we prove a constructive version of their independence result in the context of a generalization of a hierarchy of free variable logics defined by Rose [R1]. These logics are based on an axiomatized treatment of an extension by Löb and Wainer [LW] of Grzegorczyk's [G] hierarchy into the transfinite. Associated with each extended Grzegorczyk class (relative to an ordinal notation system S satisfying certain conditions) is the logic -arithmetic.

Free variable logics are interesting from the perspective of theoretical computer science. We may construe the equational definition of functions as a form of programming system. Each -arithmetic, then, has the nice property of containing both a programming system and a logic for stating and proving facts about programs.

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 1989

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References

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