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

From the 1 of 6 linked papers with an AI index.

collaborators

6 papers

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…

math.AG2025

Severi curves of rational elliptic surfaces

François Greer, Joseph Helfer, John Sheridan

We study Severi curves parametrizing rational bisections of elliptic fibrations associated to general pencils of plane cubics. Our main results show that these Severi curves are co…

math.SG2025

Exotic tight contact structures on

François-Simon Fauteux-Chapleau, Joseph Helfer

We introduce a variant of contact homology for convex open contact manifolds. As an application, we prove the existence of (in fact, infinitely many) exotic tight contact structure…

math.LO2025

Y is a least fixed point combinator

Joseph Helfer

The theory of recursive functions is related in a well-known way to the notion of *least fixed points*, by endowing a set of partial functions with an ordering in terms of their do…

math.AG2025

The integral chow ring of

Joseph Helfer, Eric Jovinelly, Eric Larson +2

This paper computes the integral Chow ring of the moduli space of stable genus 2 curves of compact type. This is done by excising boundary strata from one-by-…