proposition: Lemma realB : {in real &, forall x y, x - y \is real}.
proof: Proof. exact: rpredB. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)