Following Aehlig, we consider a hierarchy F^p= { F^p_n }_{n in Nat} of parameter-free subsystems of System F, where each F^p_n corresponds to ID_n, the theory of n-times iterated inductive definitions (thus our F^p_n corresponds to the n+1th system of Aehlig). We here present two proofs of strong normalization for F^p_n, which are directly formalizable with inductive definitions. The first one, based on the Joachimski-Matthes method, can be fully formalized in ID_n+1. This provides a tight upper bound on the complexity of the normalization theorem for System F^p_n. The second one, based on the Godel-Tait method, can be locally formalized in ID_n. This provides a direct proof to the known result that the representable functions in F^p_n are provably total in ID_n. In both cases, Buchholz' Omega-rule plays a central role.
@InProceedings{akiyoshi_et_al:LIPIcs.FSCD.2016.5, author = {Akiyoshi, Ryota and Terui, Kazushige}, title = {{Strong Normalization for the Parameter-Free Polymorphic Lambda Calculus Based on the Omega-Rule.}}, booktitle = {1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)}, pages = {5:1--5:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-010-1}, ISSN = {1868-8969}, year = {2016}, volume = {52}, editor = {Kesner, Delia and Pientka, Brigitte}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2016.5}, URN = {urn:nbn:de:0030-drops-59718}, doi = {10.4230/LIPIcs.FSCD.2016.5}, annote = {Keywords: Polymorphic Lambda Calculus, Strong Normalization, Computability Predicate, Infinitary Proof Theory} }
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