Abstract
LetL be an elementary topos. The axiom of infinity, asserting thatL has a natural numbers object, is shown to be necessary-sufficiency has long been known-for the existence of an object-classifying topos overL.
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In Memory of Evelyn Nelson
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Blass, A. Classifying topoi and the axiom of infinity. Algebra Universalis 26, 341–345 (1989). https://doi.org/10.1007/BF01211840
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DOI: https://doi.org/10.1007/BF01211840