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math.CT2026
Set-theoretic universes and paradoxes in 2-topoi
Joseph Helfer
This paper continues the development of (elementary) 2-topos theory, a foundational theory based on an axiomatization of the 2-category of categories. We prove that any 2-topos con…
math.CT2024
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…
math.CT2019
Homotopies in Grothendieck fibrations
Joseph Helfer
We define a natural 2-categorical structure on the base category of a large class of Grothendieck fibrations. Given any model category , we apply this construction to a…