proposition: Lemma edges_in1 (x : G) : edges_in [set x] = edges_at x.
proof: Proof. by rewrite /edges_in big_set1. Qed.
imports: Coq(Morphisms RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij) GraphTheory(equiv digraph setoid_bigop structures)