,
Olivier Hermant
,
Marc Aiguier
Creative Commons Attribution 4.0 International license
Higher-order logic and infinitary logic are two extensions of first-order logic that allow greater expressivity. Both features have not been investigated together yet. In this paper, we define a higher-order infinitary logic, based on an extension of simple type theory. The resulting logic features higher-order quantifiers, infinite conjunctions and infinite disjunctions. We establish results at both the syntactic and the semantic level. We introduce a sound notion of model, and we show a strong version of completeness that entails the cut-elimination theorem for natural deduction. Moreover, we prove an extension of Barr’s theorem, allowing us to constructivize classical proofs of a particular fragment of higher-order infinitary logic.
@InProceedings{traversie_et_al:LIPIcs.FSCD.2026.33,
author = {Traversi\'{e}, Thomas and Hermant, Olivier and Aiguier, Marc},
title = {{Investigations on Higher-Order Infinitary Logic}},
booktitle = {11th International Conference on Formal Structures for Computation and Deduction (FSCD 2026)},
pages = {33:1--33:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-433-8},
ISSN = {1868-8969},
year = {2026},
volume = {378},
editor = {Pfenning, Frank},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2026.33},
URN = {urn:nbn:de:0030-drops-263835},
doi = {10.4230/LIPIcs.FSCD.2026.33},
annote = {Keywords: Infinitary logic, higher-order logic, cut elimination, constructivization}
}