proposition: Lemma memv_pi1 U V w : (addv_pi1 U V) w \in U.
proof: Proof. by rewrite (subvP (diffvSl U V)) ?memv_pi. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)