∀ {𝒮 : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} 𝒮] {𝒳 : CategoryTheory.BasedCategory 𝒮}
  {𝒴 : CategoryTheory.BasedCategory 𝒮} {𝒵 : CategoryTheory.BasedCategory 𝒮} (F : CategoryTheory.BasedFunctor 𝒳 𝒴)
  {G H : CategoryTheory.BasedFunctor 𝒴 𝒵} (α : G ⟶ H),
  (CategoryTheory.BasedCategory.whiskerLeft F α).toNatTrans = F.whiskerLeft α.toNatTrans