Seminar on Sheaves and Logic,
Abstract In 1961, Jónsson and Tarski defined a certain algebraic theory with the unusual feature that its category of algebras is a topos. This is the classical Jónsson-Tarski topos. In fact, it is just one member of a whole family of 'Jónsson-Tarski toposes'; there is one such topos for each small category A and two-sided A-module M. I will introduce this family and try to put it into a wider context. I will also state some open questions.
Slides In this pdf file (500KB).
Correction: at the bottom of p.6, 'barycentric subdivision' should be ' "barycentric gluing" '.
Addition: the site AM defined at the bottom of page 5 had previously been defined by James Worrell, in A note on coalgebras and presheaves, Electronic Notes in Theoretical Computer Science 65 (2002), No. 1, 1–7.