∀ (C : Type u₁) [inst : CategoryTheory.Category.{v₁, u₁} C] (D : Type u₂) [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  (E : Type u₃) [inst_2 : CategoryTheory.Category.{v₃, u₃} E] (X : D),
  ((CategoryTheory.sum.inrCompInlCompAssociator C D E).inv.app X).down.down =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.id (Sum.inr (Sum.inl X))).down.down
      (CategoryTheory.CategoryStruct.id (Sum.inr (Sum.inl X))).down.down