proposition: Lemma deriveV f x v : f x != 0 -> derivable f x v -> 'D_v (fun y => (f y)^-1) x = - (f x) ^- 2 *: 'D_v f x.
proof: Proof. by move=> fxn0 df; apply: cvg_lim (der_inv fxn0 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