Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 403 页 · Definition and Proposition 13.68(1)
Let $f:X\to S$ be a morphism of finite type. The morphism $f$ is called projective if there exist a quasi-coherent $\mathcal O_S$-module $\mathcal E$ of finite type and a closed $S$-immersion $X\hookrightarrow\mathbb P(\mathcal E)$.