Online seminar, U. Haifa Topology & Geometry seminar on February 25, 2021

A recording of the talk is available here.

Topology & Geometry Seminar

Speaker: Julie Bergner, University of Virginia

Topic: Variants of the Waldhausen S-construction

Place: This is an online seminar. Please email David Blanc “blanc at math dot haifa dot ac dot il” for the Zoom ID and password.

Time: 16:00

Date: Thursday, February 25, 2021


The S-construction, first defined in the setting of cofibration categories by Waldhausen, gives a way to define the algebraic K-theory associated to certain kinds of categorical input.  It was proved by Galvez-Carrillo, Kock, and Tonks that the result of applying this construction to an exact category is a decomposition space, also called a 2-Segal space, and Dyckerhoff and Kapranov independently proved the same result for the slightly more general input of proto-exact categories.  In joint work with Osorno, Ozornova, Rovelli, and Scheimbauer, we proved that these results can be maximally generalized to the input of augmented stable double Segal spaces, so that the S-construction defines an equivalence of homotopy theories.  In this talk, we’ll review the S-construction and the reasoning behind these stages of generalization.  Time permitting, we’ll discuss attempts to characterize those augmented stable double Segal spaces that correspond to cyclic spaces, which is work in progress with Walker Stern.