proposition: Lemma directvP {S : proper_addv_expr} : reflect (\dim S = S :> nat) (directv S).
proof: Proof. exact: eqnP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)