proposition: Lemma ex_derive_div (f g : R -> R) (x : R) : ex_derive f x -> ex_derive g x -> g x <> 0 -> ex_derive (fun y => f y / g y) x.
proof: Proof. move => Hf Hg Hl. apply ex_derive_mult. apply Hf. by apply ex_derive_inv. Qed.
imports: Coq(Reals Psatz ssreflect) Rcomplements Rbar Lim_seq Iter Hierarchy Continuity Equiv