∀ {C : Type u_6} [inst : CategoryTheory.Category.{u_5, u_6} C] {D : Type u_3}
  [inst_1 : CategoryTheory.Category.{u_4, u_3} D] {E : Type u_1} [inst_2 : CategoryTheory.Category.{u_2, u_1} E]
  (F : CategoryTheory.Functor C (CategoryTheory.Functor D E)) (X₁ X₂ : C) (a : D),
  Subsingleton
    ((CategoryTheory.ThinSkeleton.map₂Functor F ⟦X₁⟧).obj ⟦a⟧ ⟶
      (CategoryTheory.ThinSkeleton.map₂Functor F ⟦X₂⟧).obj ⟦a⟧)