proposition: Lemma realBC x y : (x - y \is real) = (y - x \is real).
proof: Proof. exact: rpredBC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)