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2-topos 1algebraic set theory 1burali-forti paradox 1category of classes 1intuitionistic set theory 1topos sketches 1

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math.CT2026

Set-theoretic universes and paradoxes in 2-topoi

Joseph Helfer

The paper develops elementary 2‑topos theory, proves that every 2‑topos contains a model of intuitionistic ZF set theory, and shows that without size restrictions a Burali‑Forti‑ty…

math.CT2026

Internal 1-topoi in 2-topoi

Joseph Helfer

We further develop the notion of elementary 2-topos, introduced by Weber, by proposing certain new axioms. We show that in a 2-category C satisfying these axioms, the "discrete opf…