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Examining Fragments of the Quantified Propositional Calculus
Published online by Cambridge University Press: 12 March 2014
Abstract
When restricted to proving formulas, the quantified propositional proof system
is closely related to the
theorems of Buss's theory
. Namely,
has polynomial-size proofs of the translations of theorems of
, and
proves that
is sound. However, little is known about
when proving more complex formulas. In this paper, we prove a witnessing theorem for
similar in style to the KPT witnessing theorem for
. This witnessing theorem is then used to show that
proves
is sound with respect to
formulas. Note that unless the polynomial-time hierarchy collapses
is the weakest theory in the S2 hierarchy for which this is true. The witnessing theorem is also used to show that
is p-equivalent to a quantified version of extended-Frege for prenex formulas. This is followed by a proof that Gi, p-simulates
with respect to all quantified propositional formulas. We finish by proving that S2 can be axiomatized by
plus axioms stating that the cut-free version of
is sound. All together this shows that the connection between
and
does not extend to more complex formulas.
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- Research Article
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- Copyright
- Copyright © Association for Symbolic Logic 2008
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