proposition: Lemma memv_adjoin U x : x \in <<U; x>>%VS.
proof: Proof. by rewrite memvE (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)