proposition: Lemma projv_id U u : u \in U -> projv U u = u.
proof: Proof. exact: daddv_pi_id (capv_compl _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)