Cospans of finite sets

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• John Baez (University of Edinburgh, U. C. Riverside)
• Friday 31 October 2025, 14:00-15:00
• SS03, Computer Laboratory.

If you have a question about this talk, please contact Ioannis Markakis.

Cospans of finite sets are the morphisms in a bicategory, not really a category, because composition of cospans is associative only up to natural isomorphism. How can we characterize this bicategory abstractly? There’s a category of finite sets and isomorphism classes of cospans, and Steve Lack gave a beautiful characterization of this, which I will explain. But what about the bicategory? I will state a guess that I haven’t proved.

This talk is part of the Logic and Semantics Seminar (Computer Laboratory) series.

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