Basic Subtoposes of the Effective Topos

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    Abstract

    We study the lattice of local operators in Hyland’s Effective Topos. We show that this lattice is a free completion under internal sups indexed by the natural numbers object, generated by what we call basic local operators. We produce many new local operators and we employ a new concept, sight, in order to analyze these. We show that a local operator identified by A.M. Pitts in his thesis, gives a subtopos with classical arithmetic.
    Original languageEnglish
    Pages (from-to)866-883
    Number of pages18
    JournalAnnals of Pure and Applied Logic
    Volume164
    DOIs
    Publication statusPublished - 2013

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