Example 10.119.4. Consider the Noetherian local ring
R = k[[x, y]]/(y^2)
It has dimension 1 and it is Cohen-Macaulay. An example of an extension as in Lemma 10.119.3 is the extension
k[[x, y]]/(y^2) \subset k[[x, z]]/(z^2), \ \ y \mapsto xz
in other words it is gotten by adjoining y/x to R. The effect of repeating the construction n > 1 times is to adjoin the element y/x^ n.
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