proposition: Lemma subvP_adjoin U x y : y \in U -> y \in <<U; x>>%VS.
proof: Proof. exact/subvP/subv_adjoin. 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)