proposition: Lemma step_coports_ok : ports step_conodes = end_node :|: known_coports c.
proof: Proof. rewrite /step_conodes. destruct Bool.bool_dec => //. by rewrite /ports Hcond /= bigcup_setU big_set1. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix perm) ssr_ext ssralg_ext fdist subgraph_partition tanner