proposition: Lemma eq_inv_trans (w1 : seq S) (w2 : seq T) (w3 : seq U) : eq_inv w1 w2 -> eq_inv w2 w3 -> eq_inv w1 w3.
proof: Proof. rewrite /versions => H12 H23 i j. exact: (etrans (H12 i j) (H23 i j)). Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(perm fingroup) tools combclass ordtype permcomp