proposition: Lemma span_basis U X : basis_of U X -> <<X>>%VS = U.
proof: Proof. by case/andP=> /eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)