Quasi-2-Segal sets

Abstract

We show that the 2-Segal spaces (also called decomposition spaces) of Dyckerhoff-Kapranov and Gálvez-Kock-Tonks have a natural analogue within simplicial sets, which we call quasi-2-Segal sets, and that the two ideas enjoy a similar relationship as the one Segal spaces have with quasi-categories. In particular, we construct a model structure on the category of simplicial sets whose fibrant objects are the quasi-2-Segal sets which is Quillen equivalent to a model structure for complete 2-Segal spaces (where our notion of completeness comes from one of the equivalent characterizations of completeness for Segal spaces). We also prove a path space criterion, which says that a simplicial set is a quasi-2-Segal set if and only if its path spaces (also called décalage) are quasi-categories, as well as an edgewise subdivision criterion.

35 pages. v3: Accepted for publication. Corollary 7.9 and Subsection 7.1 added, discussion of Tau_2 moved to short appendix, and various other edits based on referee feedback

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Cited by in corpus (2)

• Culf maps and edgewise subdivision
• Generalizing quasi-categories via model structures on simplicial sets