(** *** Multiplicative operators *)

(* Specifications: *)
Lemma continuity_2d_pt_inv (f : R -> R -> R) (x y : R) :
continuity_2d_pt f x y ->
f x y <> 0 ->
continuity_2d_pt (fun u v => / f u v) x y.
Lemma continuity_2d_pt_mult (f g : R -> R -> R) (x y : R) :
continuity_2d_pt f x y ->
continuity_2d_pt g x y ->
continuity_2d_pt (fun u v => f u v * g u v) x y.