Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 233 页 · Definition and Proposition 9.7
A morphism of schemes $v:Y\to S$ is called separated if the following equivalent conditions are satisfied. (i) The diagonal morphism $\Delta_{Y/S}$ is a closed immersion.