fact: Definition iso_graph g := [/\ sgraph g, segmentp r1 (domain g), segmentp r2 (range g) & forall a b c d, inc (J a b) g -> inc (J c d) g -> (gle r1 a c <-> gle r2 b d)].
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)