Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 240 页 · Definition 9.31
A morphism $f:X\to Y$ of $S$-schemes is called birational if its rational equivalence class is birational. In other words, if $f$ induces an isomorphism of an open schematically dense subscheme $U$ of $X$ onto an open schematically dense subscheme $V$ of $Y$.