proposition: Lemma step_dist_it_1 lam c r t : (step_dist_it lam c r t).1 = step_it c t.
proof: Proof. rewrite /step_dist_it /step_it. elim: t c r (enum _) => //= [|a t IHt] c r [|s b] //=. by apply IHt. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix perm) ssr_ext ssralg_ext fdist subgraph_partition tanner