Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 68 页 · Proposition and Definition 3.2(1)
Let $X$ be a scheme, and $U\subseteq X$ an open subset. Then the locally ringed space $(U,\mathcal O_X|_U)$ is a scheme. We call $U$ an open subscheme of $X$.