Some uses of graphs
What sort of problem might suggest using the category of irreflexive graphs, Remember that an object of this category looks like this:
Why is this kind of picture useful? The dots may stand for physical locations and the arrows may represent roads joining them, so that this picture is a schematic road map and may be useful to plan a trip. (In practice, a two-way road is really two one way roads, separated by a patch of grass or at least a line of paint.) Dots may represent states of a physical system, and ...