Herbrand-Confluence

Stefan Hetzl, Lutz Straßburger, Arnaud Durand
2013 Logical Methods in Computer Science  
We consider cut-elimination in the sequent calculus for classical first-order logic. It is well known that this system, in its most general form, is neither confluent nor strongly normalizing. In this work we take a coarser (and mathematically more realistic) look at cut-free proofs. We analyze which witnesses they choose for which quantifiers, or in other words: we only consider the Herbrand-disjunction of a cut-free proof. Our main theorem is a confluence result for a natural class of proofs:
more » ... all (possibly infinitely many) normal forms of the non-erasing reduction lead to the same Herbrand-disjunction.
doi:10.2168/lmcs-9(4:24)2013 fatcat:hbqaglgy5jbq3ohzu6dlajskyy