proposition: Lemma differentiableM (f g : V -> R) x : differentiable f x -> differentiable g x -> differentiable (f * g) x.
proof: Proof. by move=> /differentiableP df /differentiableP dg. 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