∀ {B : Type u} [inst : CategoryTheory.Bicategory B] {a b c : B} {p : a ⟶ b} {f g : b ⟶ c} {pf : a ⟶ c} {η : f ≅ g}
  (η_f : CategoryTheory.CategoryStruct.comp p f ≅ pf) (η_g : CategoryTheory.CategoryStruct.comp p g ≅ pf),
  CategoryTheory.Bicategory.whiskerLeftIso p η ≪≫ η_g = η_f →
    CategoryTheory.Bicategory.whiskerLeftIso p η.symm ≪≫ η_f = η_g