proposition: Lemma basis_mem x U X : basis_of U X -> x \in X -> x \in U.
proof: Proof. by move/span_basis=> <- /memv_span. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)