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Jul 22, 2011 at 5:22 comment added Marc Palm I just tried to mention an example, which shows how little one knows for general discrete groups and also why vNa decomposition is probably not the best interpretation for discrete groups, since the spectrum of the free group is only one point, and it's not clear if it is the "same" point for all free groups. Does this make sense?
Jul 22, 2011 at 5:18 history edited Marc Palm CC BY-SA 3.0
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Jul 21, 2011 at 21:30 comment added Yemon Choi Lastly, I don't see why the free group factor problem is relevant to (decomposition into) irreducible representations
Jul 21, 2011 at 21:28 comment added Yemon Choi I also find the claim "Usually people talk say that the classification is just feasible for type 1 groups, which are nice to describe" somewhat unclear. (The unitary dual of certain p-adic Type I groups is, as far as I am aware, rather complicated)
Jul 21, 2011 at 21:27 comment added Yemon Choi It has long been known that for type II groups, attempts to decompose representations as direct integrals of irreducibles. This can be seen in Robert's LMSLN book (I seem to remember linking to this somewhere else on MO< but I forget where).
Jul 21, 2011 at 18:23 history edited Marc Palm CC BY-SA 3.0
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Jul 21, 2011 at 15:57 history edited Marc Palm CC BY-SA 3.0
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Jul 21, 2011 at 15:50 history edited Marc Palm CC BY-SA 3.0
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Jul 19, 2011 at 12:42 comment added Qiaochu Yuan This seems like a fairly concrete sense in which what I asked for is true; thanks for this answer. I am curious whether there is a noncompact group with discrete dual in this sense, though.
Jul 19, 2011 at 12:33 history edited Marc Palm CC BY-SA 3.0
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Jul 19, 2011 at 12:22 history edited Marc Palm CC BY-SA 3.0
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Jul 19, 2011 at 12:17 history answered Marc Palm CC BY-SA 3.0