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Model structure for double ∞-categories compatible with the square construction

Establish a model structure on bisimplicial sets that presents double ∞-categories and interacts compatibly with the square construction that sends an (∞,2)-category to a double ∞-category, thereby resolving the conjectural existence of such a model structure in the ∞-categorical setting.

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Background

The desired quasi-categorical enrichment for cosmological unstraightening on marked objects could be achieved via a model structure on s+ as above. One pathway to such a model structure would be to develop a robust model structure for double ∞-categories on bisimplicial sets that is compatible with the square construction (which associates to an (∞,2)-category a double ∞-category).

This existence was conjectured by Gaitsgory and Rozenblyum. While a corresponding result has been proven for strict double categories, the ∞-categorical analogue remains unresolved, and its resolution would likely facilitate the sought quasi-categorical enrichment.

References

The existence was already conjectured by Gaitsgory and Rozenblyum Chapter 10, Theorems 4.1.3 and 5.2.3. While the conjecture has now been settled in the case of strict double categories Theorem 6.1, the $\infty$-categorical case has remained open.

Cosmological Unstraightening (2505.16342 - Rasekh, 22 May 2025) in Section 4 (Challenges Towards A Quasi-categorically enriched cosmological Unstraightening)