proposition: Lemma root_in_Vgraph m0 n0 : n0 \in 'V(m0, n0).
proof: Proof. by rewrite /Vgraph 3!inE eqxx. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup finalg perm zmodp) mathcomp(matrix) bigop_ext ssralg_ext f2 subgraph_partition