proposition: Lemma mem_VgraphD1_Vnext n0 n1 m0 : n1 \in 'V( m0, n0) :\ n0 -> n0 \in 'V m0.
proof: Proof. rewrite 2!inE => /andP[n1n0]. by rewrite 3!inE (negbTE n1n0) orFb inE -VnextE => /andP[]. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup finalg perm zmodp) mathcomp(matrix) bigop_ext ssralg_ext f2 subgraph_partition