proposition: Lemma diffM (f g : V -> R) x : differentiable f x -> differentiable g x -> 'd (f * g) x = f x \*: 'd g x + g x \*: 'd f x :> (V -> R).
proof: Proof. by move=> /differentiableP df /differentiableP dg; rewrite diff_val. Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg ssrnum matrix interval) mathcomp(mathcomp_extra boolp classical_sets functions) reals signed topology prodnormedzmodule normedtype landau forms