proposition: Lemma subR_le0 x y : (y - x <= 0) <-> (y <= x).
proof: Proof. by split => [/leR_subl_addr|?]; [|apply/leR_subl_addr]; rewrite add0R. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum) Reals mathcomp(lra) mathcomp(Rstruct)