Abstract
LetX be a (not necessarily closed) subspace of the dual spaceB * of a separable Banach spaceB. LetX 1 denote the set of all weak* limits of sequences inX. DefineX a , for every ordinal numbera, by the inductive rule:X a = (U b < a X b ) 1 .There is always a countable ordinala such thatX a is the weak* closure ofX; the first sucha is called theorder ofX inB *.
LetE be a closed subset of a locally compact abelian group. LetPM(E) be the set of pseudomeasures, andM(E) the set of measures, whose supports are contained inE. The setE obeys synthesis if and only ifM(E) is weak* dense inPM(E). Varopoulos constructed an example in which the order ofM(E) is 2. The authors construct, for every countable ordinala, a setE inR that obeys synthesis, and such that the order ofM(E) inPM(E) isa.
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This work was done in Jerusalem, when the second-named author was a visitor at the Institute of Mathematics of the Hebrew University of Jerusalem, with the support of an NSF International Travel Grant and of NSF Grant GP33583.
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Katznelson, Y., McGehee, O.C. Some sets obeying harmonic synthesis. Israel J. Math. 23, 88–93 (1976). https://doi.org/10.1007/BF02757235
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DOI: https://doi.org/10.1007/BF02757235