proposition: Lemma diffZ (f : V -> W) k x : differentiable f x -> 'd (k *: f) x = k \*: 'd f x :> (V -> W).
proof: Proof. by move=> df; apply/diff_unique; have [] := dscale k df. 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