Maximum cuts in extended natural deduction

Abstract

We consider a standard system of sequents and a system of extended natural deduction (which is a modification of natural deduction) for intuitionistic predicate logic and connect the special cuts, maximum cuts, from sequent derivations and maximum segments from derivations of extended natural deduction. We show that the image of a sequent derivation without maximum cuts is a derivation without maximum segments (i.e., a normal derivation) in extended natural deduction.