∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  (G : CategoryTheory.Functor C D) {J : Type w} (f : J → C) [inst_2 : CategoryTheory.Limits.HasProduct f]
  [inst_3 : CategoryTheory.Limits.HasProduct fun j => G.obj (f j)]
  [inst_4 : CategoryTheory.Limits.PreservesLimit (CategoryTheory.Discrete.functor f) G],
  CategoryTheory.Limits.piComparison G f = (CategoryTheory.Limits.PreservesProduct.iso G f).hom