proposition: Lemma VnextE1 n0 m0 : n0 \in 'V m0 = tanner_rel H (inr n0) (inl m0).
proof: Proof. by rewrite /Vnext tanner_relE -lock inE. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup finalg perm zmodp) mathcomp(matrix) bigop_ext ssralg_ext f2 subgraph_partition