Definition Node' (A: Type) (l: t A) (x: option A) (r: t A): t A :=
    match l, x, r with
    | Leaf, None, Leaf => Leaf
    | _, _, _ => Node l x r
    end.

(* Specifications: *)
Lemma gnode': forall (A: Type) (l r: t A) (x: option A) (i: positive), get i (Node' l x r) = get i (Node l x r).