88th Peripatetic Seminar on
Logic, University of
Cambridge, 5 April 2009.
Summary This was a joint talk with Apostolos Matzaris. I gave the first half, and he gave the second.
In my half, I explained a new proof (and all the terminology) of the following old theorem:
Every finitary endofunctor of a locally finitely presentable category has a terminal coalgebra.
The new proof not only proves existence; it actually constructs the terminal coalgebra. It is due to Panagis Karazeris, Apostolos Matzaris, and Jiří Velebil, building on some work of my own on self-similarity.