In the excellent book "Algebraic Geometry 1" of Görtz & Wedhorn, in exercise 3.14, one is asked to show that in the spectrum of a valuation ring with infinitely many primes, the complement of the unique closed point is an open set without a closed point. It seems to me this is quite not true : to find a counter example, it is sufficient to build a valuation ring with a numerable descending chain of prime ideals, which can be done by using as value group $\mathbb{Z}^{\mathbb{N}}$ with the reverse lexicographical order. Did I miss something ?

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The answer to my question has been given by the comment of Hagen Knaf

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