∀ (B : Type u_1) [inst : CategoryTheory.Bicategory B] {a b : CategoryTheory.Bicategory.Pith B} {f g : a ⟶ b}
  (η : f ⟶ g),
  { iso := CategoryTheory.Bicategory.whiskerLeftIso (CategoryTheory.CategoryStruct.id a).of η.iso } =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.Core.isoMk (CategoryTheory.Bicategory.leftUnitor f.of)).hom
      (CategoryTheory.CategoryStruct.comp η (CategoryTheory.Core.isoMk (CategoryTheory.Bicategory.leftUnitor g.of)).inv)