∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {A F : CategoryTheory.Functor Cᵒᵖ (Type v)} (η : F ⟶ A)
  (X : C), CategoryTheory.OverPresheafAux.unitForward η X ∘ CategoryTheory.OverPresheafAux.unitBackward η X = id