proposition: Lemma eqmod_prod a b a' b': natp a -> natp b -> natp a' -> natp b' -> a = a' %c[mod B] -> b = b' %c[mod B] -> a *c b = a' *c b' %c[mod B].
proof: Proof. move=> aN bN a'N b'N e1 e2. rewrite (crem_prod aN bN) (crem_prod a'N b'N) e1 e2;reflexivity. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(binomial div)