  To foster the study of networks on an abstract level, we further study the
formalism of structured cospans. We define a topos of structured cospans and
establish its theory of rewriting. For the rewrite relation, we propose a
double categorical semantics to encode the compositionality of the structure
cospans. For an application, we generalize the inductive viewpoint of graph
rewriting to rewriting in a wider class of topoi.
