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The relative efficiency of propositional proof systems

Published online by Cambridge University Press:  12 March 2014

Stephen A. Cook  and
Robert A. Reckhow
Stephen A. Cook
Affiliation:
Department of Computer Science, University of Toronto, Toronto, CanadaM5S 1A7
Robert A. Reckhow
Affiliation:
Department of Computing Science, University of Alberta, Edmonton, CanadaT6G 2E1
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Extract

We are interested in studying the length of the shortest proof of a propositional tautology in various proof systems as a function of the length of the tautology. The smallest upper bound known for this function is exponential, no matter what the proof system. A question we would like to answer (but have not been able to) is whether this function has a polynomial bound for some proof system. (This question is motivated below.) Our results here are relative results.

In §§2 and 3 we indicate that all standard Hilbert type systems (or Frege systems, as we call them) and natural deduction systems are equivalent, up to application of a polynomial, as far as minimum proof length goes. In §4 we introduce extended Frege systems, which allow introduction of abbreviations for formulas. Since these abbreviations can be iterated, they eliminate the need for a possible exponential growth in formula length in a proof, as is illustrated by an example (the pigeonhole principle). In fact, Theorem 4.6 (which is a variation of a theorem of Statman) states that with a penalty of at most a linear increase in the number of lines of a proof in an extended Frege system, no line in the proof need be more than a constant times the length of the formula proved.

Type
Research Article
Information
The Journal of Symbolic Logic , Volume 44 , Issue 1 , March 1979 , pp. 36 - 50
Copyright
Copyright © Association for Symbolic Logic 1979

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References

REFERENCES

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