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This paper tries to remove what seems to be the remaining stumbling blocks in the way to a full understanding of the Curry-Howard isomorphism for sequent calculus, namely the questions: What do variables in proof terms stand for? What is co-control and a co-continuation? How to define the dual of Parigot's mu-operator so that it is a co-control operator? Answering these questions leads to the interpretation that sequent calculus is a formal vector notation with first-class co-control. But this is just the "internal" interpretation, which has to be developed simultaneously with, and is justified by, an equivalent, "external" interpretation, offered by natural deduction: the sequent calculus corresponds to a bi-directional, agnostic (w.r.t. the call strategy), computational lambda-calculus. Next, the formal duality between control and co-control is studied, in the context of classical logic. The duality cannot be observed in the sequent calculus, but rather in a system unifying sequent calculus and natural deduction.
@InProceedings{espiritosanto:LIPIcs.TLCA.2015.165,
author = {Esp{\'\i}rito Santo, Jos\'{e}},
title = {{Curry-Howard for Sequent Calculus at Last!}},
booktitle = {13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015)},
pages = {165--179},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-87-3},
ISSN = {1868-8969},
year = {2015},
volume = {38},
editor = {Altenkirch, Thorsten},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TLCA.2015.165},
URN = {urn:nbn:de:0030-drops-51626},
doi = {10.4230/LIPIcs.TLCA.2015.165},
annote = {Keywords: co-control, co-continuation, vector notation, let-expression, formal sub- stitution, context substitution, computational lambda-calculus, classical lo}
}