22 June 2006 (Thursday) 

1:00 - 2:30   Thorsten Palm

Polytopic Sets and Categories with Slicing.
 
Abstract:
 
A formalization of Makkai's concept of a multitopic set, taking
seriously the accompanying geometric idea, has led to the
transitional notion of a polytopic set, which is of interest in
its own right. While multitopic sets form a presheaf category,
polytopic sets do not; I shall describe the precise extent of this
failure. 
 
An appropriately modified description applies to a wide variety
of situations. This is where the new notion of a category with
slicing enters the picture. I shall give the definition and examples, 
among which the category of multitopic sets and the category of
polytopic sets are the primary ones.