Abstract
In my three-part paper "Generalized sketches as a framework for
completeness theorems" (JPAA 1997), I construct, for each of a number
of categorical doctrines, call it D, a presheaf category C such that
D is the full subcategory of C with objects that are injective
relative to a small, usually finite, number of arrows, the
"sketch-axioms", in C ; the set of the sketch-axioms I denote by A
. For example, if D is the category of small finite-limit categories
(with arrows the functors preserving finite limits in the non-strict
sense), than C is the category (with suitable arrows!) of
finite-limit sketches. In each of the examples of D , one has two
weak factorization systems (the factoring diagonal is not required to
be unique), one of them giving rise, using the above set A of
"sketch-axioms" to the objects of D as the Kan complexes arise as
the fibrant objects, from the horn-extensions in the Quillen model
structure on simplicial sets. I am interested in the question for
which of my examples of sketch-categories C the two factorization
systems determine a Quillen model structure; in some simple cases, I
already know that this is case. In the sketch-categories, the strict
anodyne maps play a distinguished role. These are the ones that, in
the classical case of simplicial sets, are obtained from the
Gabriel-Zisman definition of anodyne map by omitting reference to
retracts. In the sketch-category C, the strict anodyne maps are the
transfinite composites of pushouts of the sketch-axioms, the arrows in
the set A . (In the classical case also, the strict anodynes are the
transfinite composites of the pushouts of the horn-extensions.) In
the talk, I will start with discussing the classical case of the
category of simplicial sets with a special emphasis on the strict
anodyne maps, and a variant of the latter related to Andre Joyal's
model structure on simplicial sets where the fibrant object are the
quasi-categories.