proposition: Lemma step_edges_ok x : step_edges x = if x == start_port then end_port else edges c x.
proof: Proof. by rewrite /step_edges Htriv Hcond ffunE. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix perm) ssr_ext ssralg_ext fdist subgraph_partition tanner