proposition: Lemma csum_Mlteq a a' b: natp b -> a <c a' -> (a +c b) <c (a'+c b).
proof: Proof. by move=> bN aa'; rewrite csumC (csumC a' b); apply: csum_Meqlt. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(binomial div)