∀ {C : Type u₁} {D : Type u₂} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  [inst_2 : CategoryTheory.Preadditive C] [inst_3 : CategoryTheory.Preadditive D] {F : CategoryTheory.Functor C D}
  {G : CategoryTheory.Functor D C} (adj : F ⊣ G) [F.Additive] (X : C) (Y : D), (adj.homEquiv X Y) 0 = 0