Schur's property: Difference between revisions
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In [[algebraic topology]], a branch of [[mathematics]], the '''Čech-to-derived functor spectral sequence''' is a [[spectral sequence]] that relates [[Čech cohomology]] of a [[sheaf (mathematics)|sheaf]] and [[sheaf cohomology]].{{sfn|Dimca|2004|loc=2.3.9}} | |||
Let <math>\mathcal{F}</math> be a sheaf on a topological space ''X''. Choose an open cover <math>\mathfrak{U}</math> of ''X''. That is, <math>\mathfrak{U}</math> is a set of open subsets of ''X'' which together cover ''X''. Let <math>\mathcal{H}^q(X, \mathcal{F})</math> denote the presheaf which takes an open set ''U'' to the ''q''th cohomology of <math>\mathcal{F}</math> on ''U'', that is, to <math>H^q(U, \mathcal{F})</math>. For any presheaf <math>\mathcal{G}</math>, let <math>\check{H}^p(\mathfrak{U}, \mathcal{G})</math> denote the ''p''th Čech cohomology of <math>\mathcal{G}</math> with respect to the cover <math>\mathfrak{U}</math>. Then the Čech-to-derived functor spectral sequence is:{{sfn|Godement|1973|loc=Théorème 5.4.1}} | |||
:<math>E^{p,q}_2 = \check{H}^p(\mathfrak{U}, \mathcal{H}^q(X, \mathcal{F})) \Rightarrow H^{p+q}(X, \mathcal{F}).</math> | |||
If <math>\mathfrak{U}</math> consists of only two open sets, then this spectral sequence degenerates to the [[Mayer–Vietoris sequence]]. See [[Spectral sequence#Long exact sequences]]. | |||
If for all finite intersections of a covering the cohomology vanishes, the ''E''<sub>''2''</sub>-term degenerates and the edge morphisms yield an isomorphism of Čech cohomology for this covering to sheaf cohomology. This provides a method of computing sheaf cohomology using Čech cohomology. For instance, this happens if <math>\mathcal{F}</math> is a quasi-coherent sheaf on a [[scheme (mathematics)|scheme]] and each element of <math>\mathfrak{U}</math> is an open affine subscheme such that all finite intersections are again affine (e.g. if the scheme is [[separated scheme|separated]]). This can be used to compute the cohomology of line bundles on projective space.{{sfn|Hartshorne|1977|loc=Theorem III.5.1}} | |||
== See also == | |||
* [[Leray's theorem]] | |||
==Notes== | |||
{{reflist}} | |||
==References== | |||
*{{Citation | |||
| last=Dimca | |||
| first=Alexandru | |||
| title=Sheaves in topology | |||
| publisher=[[Springer-Verlag]] | |||
| year=2004 | |||
| location=Berlin | |||
| series=Universitext | |||
| isbn=978-3-540-20665-1 | |||
| mr=2050072 | |||
}} | |||
* {{Citation | |||
| last1=Godement | |||
| first1=Roger | |||
| author1-link=Roger Godement | |||
| title=Topologie algébrique et théorie des faisceaux | |||
| publisher=Hermann | |||
| location=Paris | |||
| mr=0345092 | |||
| year=1973}} | |||
* {{Hartshorne AG}} | |||
{{DEFAULTSORT:Cech-To-Derived funcTor Spectral Sequence}} | |||
[[Category:Spectral sequences]] | |||
{{topology-stub}} |
Revision as of 22:58, 19 June 2013
In algebraic topology, a branch of mathematics, the Čech-to-derived functor spectral sequence is a spectral sequence that relates Čech cohomology of a sheaf and sheaf cohomology.Template:Sfn
Let be a sheaf on a topological space X. Choose an open cover of X. That is, is a set of open subsets of X which together cover X. Let denote the presheaf which takes an open set U to the qth cohomology of on U, that is, to . For any presheaf , let denote the pth Čech cohomology of with respect to the cover . Then the Čech-to-derived functor spectral sequence is:Template:Sfn
If consists of only two open sets, then this spectral sequence degenerates to the Mayer–Vietoris sequence. See Spectral sequence#Long exact sequences.
If for all finite intersections of a covering the cohomology vanishes, the E2-term degenerates and the edge morphisms yield an isomorphism of Čech cohomology for this covering to sheaf cohomology. This provides a method of computing sheaf cohomology using Čech cohomology. For instance, this happens if is a quasi-coherent sheaf on a scheme and each element of is an open affine subscheme such that all finite intersections are again affine (e.g. if the scheme is separated). This can be used to compute the cohomology of line bundles on projective space.Template:Sfn
See also
Notes
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References
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Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
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15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
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