 For instance, the category Grph of graphs of the kind permitting multiple directed edges between two vertices is a topos.A graph consists of two sets, an edge set and a vertex set, and two functions "s,t" between those sets, assigning to every edge "e" its source "s"("e") and target "t"("e").Grph is thus equivalent to the functor category Set"C", where "C" is the category with two objects "E" and "V" and two morphisms "s,t"