[Rencontre] The event is canceled, March 9, 2023
In relation with the current social movement about the reform of pensions, the planned meeting is canceled   voir la motion adoptÃ©e par le GT Scalp.
Programme

Peter Dybjer (Chalmers Univ. (Sweden))
We give a new syntax independent definition of the notion of a generalized algebraic theory as an initial object in a category of categories with families (cwfs) with extra structure. To this end we define inductively how to build a valid signature $\Sigma$ for a generalized algebraic theory and the associated category $\Cwf_\Sigma$ of cwfs with a $\Sigma$structure and cwfmorphisms that preserve this structure on the nose. Our definition refers to {\em uniform families} of contexts, types, and terms, a purely semantic notion. Furthermore, we show how to syntactically construct initial cwfs with $\Sigma$structures. This result can be viewed as a generalization of Birkhoff's completeness theorem for equational logic. It is obtained by extending Castellan, Clairambault, and Dybjer's construction of an initial cwf. We provide examples of generalized algebraic theories for monoids, categories, categories with families, and categories with families with extra structure for some type formers of dependent type theory. The models of these are internal monoids, internal categories, and internal categories with families (with extra structure) in a category with families.

Axel Kerinec (LIPN)Invited talk: TBA

Gabriele Vanoni (INRIA)Invited talk: TBA