The Stacks project

Lemma 28.13.4. Let $X$ be an integral scheme. The following are equivalent:

1. The scheme $X$ is Japanese.

2. For every affine open $U \subset X$ the domain $\mathcal{O}_ X(U)$ is Japanese.

3. There exists an affine open covering $X = \bigcup U_ i$ such that each $\mathcal{O}_ X(U_ i)$ is Japanese.

4. There exists an open covering $X = \bigcup X_ j$ such that each open subscheme $X_ j$ is Japanese.

Moreover, if $X$ is Japanese then every open subscheme is Japanese.