(*D11*)
 Definition sub (x y : canonTree) : option canonTree :=
  match eq_dec (glb x y) y with
  | left _ => Some (glb x (comp y))
  | right _ => None
  end.

Lemma unrel_right_obmit: forall a a1 a2 t1 t2 c c1, t1 <> Leaf false -> decompose a = (a1,a2) -> unrel (exist _ (Node t1 t2) c) a = unrel (exist _ t1 c1) a1.