Lemma 27.8.3. Let $X$ be a scheme. The following are equivalent:

The scheme $X$ is Cohen-Macaulay.

For every affine open $U \subset X$ the ring $\mathcal{O}_ X(U)$ is Noetherian and Cohen-Macaulay.

There exists an affine open covering $X = \bigcup U_ i$ such that each $\mathcal{O}_ X(U_ i)$ is Noetherian and Cohen-Macaulay.

There exists an open covering $X = \bigcup X_ j$ such that each open subscheme $X_ j$ is Cohen-Macaulay.

Moreover, if $X$ is Cohen-Macaulay then every open subscheme is Cohen-Macaulay.

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