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In [[algebraic geometry]], an '''fpqc morphism''' <math>f: X \to Y</math> of schemes is a [[faithfully flat morphism]] that satisfies the following equivalent conditions: | |||
# Every [[quasi-compact]] open subset of Y is the image of a quasi-compact open subset of ''X''. | |||
# There exists a covering <math>V_i</math> of Y by open affine subschemes such that each <math>V_i</math> is the image of a quasi-compact open subset of X. | |||
# Each point <math>x \in X</math> has a neighborhood <math>U</math> such that <math>f(U)</math> is open and <math>f: U \to f(U)</math> is [[quasi-compact morphism|quasi-compact]]. | |||
# Each point <math>x \in X</math> has a quasi-compact neighborhood such that <math>f(U)</math> is open affine. | |||
Examples: An open faithfully flat morphism is fpqc. | |||
An fpqc morphism satisfies the following properties: | |||
* The composite of fpqc morphisms is fpqc. | |||
* A base change of an fpqc morphism is fpqc. | |||
* If <math>f: X \to Y</math> is a morphism of schemes and if there is an open covering <math>V_i</math> of ''Y'' such that the <math>f: f^{-1}(V_i) \to V_i</math> is fpqc, then ''f'' is fpqc. | |||
* A faithfully flat morphism that is locally of finite presentation (i.e., fppf) is fpqc. | |||
* If <math>f:X \to Y</math> is an fpqc morphism, a subset of ''Y'' is open in Y if and only if its inverse image under ''f'' is open in X. | |||
== See also == | |||
* [[flat topology]] | |||
* [[fppf morphism]] | |||
* [[quasi-compact morphism]] | |||
== References == | |||
*Angelo Vistoli, "Notes on Grothendieck topologies, fibered categories and descent theory." {{arxiv|id=0412512v4|archive=math.AG}} | |||
{{geometry-stub}} | |||
[[Category:Morphisms of schemes]] |
Revision as of 17:47, 26 January 2014
Template:Lowercase title In algebraic geometry, an fpqc morphism of schemes is a faithfully flat morphism that satisfies the following equivalent conditions:
- Every quasi-compact open subset of Y is the image of a quasi-compact open subset of X.
- There exists a covering of Y by open affine subschemes such that each is the image of a quasi-compact open subset of X.
- Each point has a neighborhood such that is open and is quasi-compact.
- Each point has a quasi-compact neighborhood such that is open affine.
Examples: An open faithfully flat morphism is fpqc.
An fpqc morphism satisfies the following properties:
- The composite of fpqc morphisms is fpqc.
- A base change of an fpqc morphism is fpqc.
- If is a morphism of schemes and if there is an open covering of Y such that the is fpqc, then f is fpqc.
- A faithfully flat morphism that is locally of finite presentation (i.e., fppf) is fpqc.
- If is an fpqc morphism, a subset of Y is open in Y if and only if its inverse image under f is open in X.
See also
References
- Angelo Vistoli, "Notes on Grothendieck topologies, fibered categories and descent theory." Template:Arxiv
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