Abstract
We use topos-theoretic methods to show that intuitionistic set theory with countable or dependent choice does not imply that every family, all of whose elements are doubletons and which has at most one element, has a choice function.
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Fourman, M.P., Ščedrov, A. The “world's simplest axiom of choice” fails. Manuscripta Math 38, 325–332 (1982). https://doi.org/10.1007/BF01170929
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DOI: https://doi.org/10.1007/BF01170929