proposition: Fact ffun_scale_addl u : {morph (ffun_scale)^~ u : k1 k2 / k1 + k2}.
proof: Proof. by move=> k1 k2; apply/ffunP=> a; rewrite !ffunE scalerDl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)