∀ {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), ac.equiv (Sum.inl i₁) = e₁.f i₁