∀ {I₁ : Type u_1} {I₂ : Type u_2} {I₁₂ : Type u_4} {c₁ : ComplexShape I₁} (c₂ : ComplexShape I₂)
  (c₁₂ : ComplexShape I₁₂) [inst : TotalComplexShape c₁ c₂ c₁₂] {i₁ i₁' : I₁},
  c₁.Rel i₁ i₁' → ∀ (i₂ : I₂), c₁₂.Rel (c₁.π c₂ c₁₂ (i₁, i₂)) (c₁.π c₂ c₁₂ (i₁', i₂))