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De Morgan classifying toposes

Research paper by Olivia Caramello

Indexed on: 11 Aug '08Published on: 11 Aug '08Published in: Mathematics - Category Theory



Abstract

We present a general method for deciding whether a Grothendieck topos satisfies De Morgan's law (resp. the law of excluded middle) or not; applications to the theory of classifying toposes follow. Specifically, we obtain a syntactic characterization of the class of geometric theories whose classifying toposes satisfy De Morgan's law (resp. are Boolean), as well as model-theoretic criteria for theories whose classifying toposes arise as localizations of a given presheaf topos.