proposition: Lemma subv_trans : transitive subV.
proof: Proof. by move=> U V W /subvP sUV /subvP sVW; apply/subvP=> u /sUV/sVW. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)