Exercise 22, § 4

Let $A$ be a noetherian ring, $a$ an ideal of $A$ distinct from $A$. Suppose that $A$ is separated and complete for the $a$-adic topology, and that $A/a$ is a Nagata ring. Then every ring of restricted formal power series in a finite number of indeterminates is a Nagata ring. (Use III, § 4, Exercise 7, and Exercises 20 and 21 above.)