Finite morphism
（重定向自Morphism of finite type）
In algebraic geometry, a morphism f: X → Y of schemes is a finite morphism if Y has an open cover by affine schemes
such that for each i,
is an open affine subscheme Spec Ai, and the restriction of f to Ui, which induces a ring homomorphism
makes Ai a finitely generated module over Bi. One also says that X is finite over Y.