fact: Definition edge_surjective (G1 G2 : sgraph) (h : G1 -> G2) := forall x y : G2 , x -- y -> exists x0 y0, [/\ h x0 = x, h y0 = y & x0 -- y0].
imports: Coq(RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph) GraphTheory(sgraph treewidth set_tac)