Abstract
Let R be any ring (with 1), G a torsion free group and R G the corresponding group ring. Let ExtR G* (M, M) be the cohomology ring associated with the R G-module M. Let H be a subgroup of finite index of G. The following is a special version of our main Theorem: Assume the profinite completion of G is torsion free. Then an element ζ ∈ ExtR G* (M, M) is nilpotent (under Yoneda's product) if and only if its restriction to ExtR H* (M, M) is nilpotent. In particular this holds for the Thompson group. There are torsion free groups for which the analogous statement is false.
Original language | English |
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Pages (from-to) | 1099-1102 |
Number of pages | 4 |
Journal | Journal of Pure and Applied Algebra |
Volume | 208 |
Issue number | 3 |
DOIs | |
State | Published - Mar 2007 |
Externally published | Yes |