∀ (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 : E),
  ((CategoryTheory.sum.inrCompInrCompInverseAssociator C D E).hom.app X).down =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.id (Sum.inr X)).down
      (CategoryTheory.CategoryStruct.id (Sum.inr X)).down