proposition: Lemma seqv_sub_adjoin U xs : {subset xs <= <<U & xs>>%VS}.
proof: Proof. by apply/span_subvP; rewrite (subv_trans (sub_agenv _)) ?agenvS ?addvSr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype div tuple finfun bigop ssralg) mathcomp(finalg zmodp matrix vector poly)