∀ {A : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} A] {A' : Type u_2}
  [inst_1 : CategoryTheory.Category.{v_2, u_2} A'] {B : Type u} [inst_2 : CategoryTheory.Category.{v, u} B]
  (X : CategoryTheory.Functor A B × CategoryTheory.Functor A' B) (X_1 : A),
  (CategoryTheory.Sum.functorEquivInverseCompWhiskeringLeftInlIso.inv.app X).app X_1 =
    CategoryTheory.CategoryStruct.id (X.1.obj X_1)