2-Segal sets and the Waldhausen construction

TL;DR

This paper establishes an equivalence between augmented stable double categories and unital 2-Segal sets, providing explicit constructions and illustrating with examples from various mathematical structures.

Contribution

It proves a new categorical equivalence linking stable double categories and 2-Segal sets, expanding understanding of the Waldhausen construction's structure.

Findings

Proves the equivalence between augmented stable double categories and unital 2-Segal sets.

Provides an explicit inverse via a path construction.

Illustrates the equivalence with examples like partial monoids and cobordism categories.

Abstract

It is known by results of Dyckerhoff-Kapranov and of G\'alvez--Carrillo-Kock-Tonks that the output of the Waldhausen S.-construction has a unital 2-Segal structure. Here, we prove that a certain S.-functor defines an equivalence between the category of augmented stable double categories and the category of unital 2-Segal sets. The inverse equivalence is described explicitly by a path construction. We illustrate the equivalence for the known examples of partial monoids, cobordism categories with genus constraints and graph coalgebras.