∀ {ι : Type u_1} {ι₁ : Type u_2} {ι₂ : Type u_3} {c : ComplexShape ι} {c₁ : ComplexShape ι₁} {c₂ : ComplexShape ι₂}
  {e₁ : c₁.Embedding c} {e₂ : c₂.Embedding c} {ac : e₁.AreComplementary e₂} {i₁ : ι₁} {i₂ : ι₂},
  ac.Boundary i₁ i₂ → e₁.BoundaryLE i₁