proposition: Lemma diffN (f : V -> W) x : differentiable f x -> 'd (- f) x = - ('d f x : V -> W) :> (V -> W).
proof: Proof. move=> df; rewrite -[RHS]/(@GRing.opp _ \o _); apply/diff_unique; by have [] := dopp 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