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Andreas Fjellstad | A note on the cut-elimination proof in "Truth without contra(di)ction" | The Review of Symbolic Logic
A note on the cut-elimination proof in "Truth without contra(di)ction"
This note shows that the permutation instructions presented by Zardini (2011) for eliminating cuts on universally quantified formulas in the sequent calculus for the noncontractive theory of truth IKTω are inadequate. To that purpose the note presents a derivation in the sequent calculus for IKTω ending with an application of cut on a universally quantified formula which the permutation instructions cannot deal with. The counterexample is of the kind that leaves open the question whether cut can be shown to be eliminable in the sequent calculus for IKTω with an alternative strategy.
KEYWORDS: noncontractive theory of truth, cut-elimination, sequent calculus, infinitary sequents