∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {X Y : C} (c : CategoryTheory.Limits.BinaryFan X Y)
  (l : CategoryTheory.Limits.WalkingPair),
  c.π.app { as := l } =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.Iso.refl c.pt).hom
      ((CategoryTheory.Limits.BinaryFan.mk c.fst c.snd).π.app { as := l })