proposition: Lemma BRsum_Mlelt0 a b c : a <=r c -> b <r \0r -> (a +r b) <r c.
proof: Proof. by move => pa pb; move: (BRsum_Mlelt pa pb); rewrite (BRsum_0r (proj32 pa)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)