Ultrafinitism postulates that we can only compute on relatively short objects, and numbers beyond a certain value are not available. This approach would also forbid many forms of infinitary reasoning and allow removing certain paradoxes stemming from enumeration theorems. For a computational application of ultrafinitist logic, we need more than a proof system, but a logical framework to express both proofs, programs, and theorems in a single framework. We present its inference rules, reduction relation, and self-encoding to allow direct proving of the properties of ultrafinitist logic within itself. We also provide a justification why it can express all bounded Turing programs, and thus serve as a "logic of computability".
@InProceedings{gajda:LIPIcs.TYPES.2023.5, author = {Gajda, Micha{\l} J.}, title = {{Consistent Ultrafinitist Logic}}, booktitle = {29th International Conference on Types for Proofs and Programs (TYPES 2023)}, pages = {5:1--5:20}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-332-4}, ISSN = {1868-8969}, year = {2024}, volume = {303}, editor = {Kesner, Delia and Reyes, Eduardo Hermo and van den Berg, Benno}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2023.5}, URN = {urn:nbn:de:0030-drops-204833}, doi = {10.4230/LIPIcs.TYPES.2023.5}, annote = {Keywords: ultrafinitism, bounded Turing completeness, logic of computability, decidable logic, explicit complexity, strict finitism} }
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