
Venue
85th Peripatetic
Seminar on Sheaves and Logic,
Nice,
24/3/07
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 JónssonTarski topos. In fact, it is just one member of a whole family of 'JónssonTarski toposes'; there is one such topos for each small category A and twosided Amodule 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 A_{M} 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.
