A Krengel-type theorem for finitely generated nilpotent groups
نویسندگان
چکیده
has density one in Z with respect to some sequence of intervals Ik = [ak, bk] with bk−ak → ∞. (This means that d{Ik}(S) = lim k→∞ |S∩Ik| bk−ak+1 = 1.) A vector f ∈ H is called weakly wandering if there is an infinite set S ⊆ Z such that for any n,m ∈ S, n 6= m, one has 〈Uf, Uf〉 = 0. The following theorem due to U. Krengel gives a characterization of weak mixing in terms of weakly wandering vectors.
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تاریخ انتشار 1999