proposition: Lemma nil_free : free (Nil vT).
proof: Proof. by rewrite /free span_nil dimv0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)