∀ {ι : Type u_1} {ι' : Type u_2} (c : ComplexShape ι) (c' : ComplexShape ι') (f : ι → ι') (hf : Function.Injective f)
  (iff : ∀ (i₁ i₂ : ι), c.Rel i₁ i₂ ↔ c'.Rel (f i₁) (f i₂)), (ComplexShape.Embedding.mk' c c' f hf iff).IsRelIff