Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 348 页 · Definition 12.55
A morphism of schemes $f:X\to Y$ is called proper (or $X$ is called proper over $Y$) if $f$ is of finite type, separated and universally closed.