∀ (f : ZFSet.{u_1} → ZFSet.{u_1}) [inst : ZFSet.Definable₁ f] (n : ℕ) (g : (Fin n → ZFSet.{u_1}) → ZFSet.{u_1})
  [inst_1 : ZFSet.Definable n g] (xs : Fin n → PSet.{u_1}),
  ZFSet.mk (ZFSet.Definable₁.out f (ZFSet.Definable.out g xs)) = f (g fun x => ZFSet.mk (xs x))