proposition: Lemma derivableV f (x v : V) : f x != 0 -> derivable f x v -> derivable (fun y => (f y)^-1) x v.
proof: Proof. move=> df dg; apply/cvg_ex; exists (- (f x) ^- 2 *: 'D_v f x). exact: der_inv. 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