Co-Localization, Co-Support and Local Homology
Co-Localization, Co-Support and Local Homology
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共定位、共支持和局部同源
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发表时间:
2006
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通讯作者:
A. S. Richardson
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作者:
A. S. Richardson
We propose a definition of co-support for modules over commutative, Noetherian rings that we hope will relate to the local homology functors of Greenlees and May in the same way ordinary support relates to local cohomology. By expressing local homology in terms of the Koszul complex, we prove some vanishing theorems involving this co-support. We also investigate the co-localization functor which gives rise to our definition of co-support. This functor treats Artiniantype constructions the same way the ordinary localization functor treats Noetherian-type constructions, and this duality extends to one between co-support and ordinary support. Introduction. Given a module M over a commutative, Noetherian ring A and an ideal I of A, if we attempt to restrict the support of M to the variety V (I), that amounts to taking the I-adic torsion of M . The right derived functors of this process are the local cohomology functors H• I . The concept of support is thus part of local cohomology from the beginning. It also shows up in certain well-known vanishing results: If M is torsion to begin with, which is to say if Supp M ⊂ V (I), then all the higher local cohomology modules of M vanish. Furthermore, the local cohomology of any module M will always vanish past the dimension of the support of M . In [8], Matlis defined the local homology functors to be the left derived functors of the I-adic completion functor. Since torsion and completion are dual, one expects these functors to live up to their name and behave in a manner dual to local cohomology. In particular, it is natural to expect there to be vanishing theorems for local homology dual to the ones that relate the local cohomology of a module to the module’s support. Before we can prove or even state such theorems, however, we have to decide how to dualize the notion of support. That is the primary objective of this paper. AMS Mathematics Subject Classification. Primary 13D07, 13E10. Received by the editors on June 20, 2003, and in revised form on January 6, 2004. Copyright c ©2006 Rocky Mountain Mathematics Consortium