Definition 10.121.2. Suppose that K is a field, and R \subset K is a local1 Noetherian subring of dimension 1 with fraction field K. In this case we define the order of vanishing along R
\text{ord}_ R : K^* \longrightarrow \mathbf{Z}
by the rule
\text{ord}_ R(x) = \text{length}_ R(R/(x))
if x \in R and we set \text{ord}_ R(x/y) = \text{ord}_ R(x) - \text{ord}_ R(y) for x, y \in R both nonzero.
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