Date: Wed, 13 Dec 1995 10:01:02 -0400 (AST)
Subject: Discrete opfibrations of graphs

Date: Sun, 10 Dec 1995 19:52:30 +0100 (MET)
From: Sebastiano Vigna <vigna@colos3.usr.dsi.unimi.it>

Suppose you have coloured graphs G,H (with multiple edges,
etc. i.e., we are in the topos of coloured graphs). A morphism
G->H induces a functor between the free categories generated
by G and H. I am interested in those morphisms which induce
discrete opfibrations. Has anyone studied this notion?
Essentially, any arc f(x)->y of H can be lifted uniquely
to an arc (with the same label) x->x', for some x' such
that f(x')=y.


                                        Sebastiano Vigna