I’m giving a talk entitled “Terms for Classical Sequents: Proof Invariants and Strong Normalisation” at the University of Gothenburg Logic Seminar, via Skype.

Abstract: A proof for a sequent \(\Sigma\vdash\Delta\) shows you how to get from the premises \(\Sigma\) to the conclusion \(\Delta\). It seems very plausible that some valid sequents have *different* proofs. It also seems plausible that some different derivations for the one sequent don’t represent different proofs, but are merely different ways to present the *same* proof. These two plausible ideas are hard to make precise, especially in the case of classical logic.

In this paper, I give a new account of a kind of invariant for derivations in the classical sequent calculus, and show how it can formalise a notion of proof identity with pleasing behaviour. In particular, it has a confluent, strongly normalising cut elimination procedure.

I’m *Greg Restall*, and this is my personal website. ¶ I am the Shelby Cullom Davis Professor of Philosophy at the University of St Andrews.

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