Bourbaki

Example 2

Tag 0CWZ, permanent. Cite it as [Bourbaki, Tag 0CWZ].

Commutative Algebra, chapter IX, § 2. Anneaux de Cohen

Let A be an integral, separated and complete local ring. Suppose that the residue field kk of A is finite, with q=pfq = p^f elements, hence perfect of characteristic pp. We have xq=xx^q = x for every x∈kx \in k, whence sq=ss^q = s for every multiplicative representative s. It follows that the set of multiplicative representatives consists of 0 and the q−1q - 1 (q−1)(q - 1)-th roots of unity in the field of fractions of A. If the field of fractions of A is locally compact, the existence of multiplicative representatives also follows from VI, § 9, No. 2, Proposition 3 (cf. also VI, § 9, Exercise 5).

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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