proposition: Lemma addv_pi2_id U V v : v \in V -> addv_pi2 U V v = v.
proof: Proof. by apply: daddv_pi_id; rewrite capvC capv_diff. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)