# non discrete valuation ring [closed]

Hi, I am looking for examples of non-discrete valuation rings. Could you help me? Thanks

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## closed as off topic by Martin Brandenburg, Qiaochu Yuan, Sándor Kovács, Mark Sapir, Ben Webster♦Feb 2 '11 at 21:20

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Please read the FAQ; this question does not seem to be appropriate for MO. Anyway I give you a hint: Open a book which treats valuation rings, there are many examples. – Martin Brandenburg Feb 2 '11 at 17:28
Here is a good example: Let $k$ be a field and consider the field of formal power series $\sum_{i \in I} a_i t^i$ where $I$ can be any well-ordered en.wikipedia.org/wiki/Well_ordered subset of $\mathbb{R}$. Sum and product are defined formally by $\sum (a_i+b_i) t^i$ and $\sum a_i b_j t^{i+j}$. Exercise: The sum or product of two formal power series of this form is another one, and every coefficient of the sum or product is a finite polynomial in the coefficents of the summands/multiplicands. The valuation is $v(\sum a_i t^i) = \min(i : a_i \neq 0)$. – David Speyer Feb 2 '11 at 18:10