proposition: Lemma fmorph_div : {morph f : x y / x / y}.
proof: Proof. by move=> x y; rewrite rmorphM /= fmorphV. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)