Characterising Complexity Classes by Inductive Definitions in Bounded Arithmetic

Abstract

Famous descriptive characterisations of P and PSPACE are restated in terms of the Cook-Nguyen style second order bounded arithmetic. We introduce an axiom of inductive definitions over second order bounded arithmetic. We show that P can be captured by the axiom of inflationary inductive definitions whereas PSPACE can be captured by the axiom of non-inflationary inductive definitions.