According to the standard, non type-theoretic accounts of Bishop’s constructivism (BISH), dependent functions are not necessary to BISH. Dependent functions though, are explicitly used by Bishop in his definition of the intersection of a family of subsets, and they are necessary to the definition of arbitrary products. In this paper we present the basic notions and principles of CSFT, a semi-formal constructive theory of sets and functions intended to be a minimal, adequate and faithful, in Feferman’s sense, semi-formalisation of Bishop’s set theory (BST). We define the notions of dependent sum (or exterior union) and dependent product of set-indexed families of sets within CSFT, and we prove the distributivity of prod over sum i.e., the translation of the type-theoretic axiom of choice within CSFT. We also define the notions of dependent sum (or interior union) and dependent product of set-indexed families of subsets within CSFT. For these definitions we extend BST with the universe of sets #1 V_0 and the universe of functions #1 V_1.
@InProceedings{petrakis:LIPIcs.TYPES.2018.3, author = {Petrakis, Iosif}, title = {{Dependent Sums and Dependent Products in Bishop’s Set Theory}}, booktitle = {24th International Conference on Types for Proofs and Programs (TYPES 2018)}, pages = {3:1--3:21}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-106-1}, ISSN = {1868-8969}, year = {2019}, volume = {130}, editor = {Dybjer, Peter and Esp{\'\i}rito Santo, Jos\'{e} and Pinto, Lu{\'\i}s}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2018.3}, URN = {urn:nbn:de:0030-drops-114070}, doi = {10.4230/LIPIcs.TYPES.2018.3}, annote = {Keywords: Bishop’s constructive mathematics, Martin-L\"{o}f’s type theory, dependent sums, dependent products, type-theoretic axiom of choice} }
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