Abstract
We prove that every PS-ultrafilter on a group without second-order elements is a Ramsey ultrafilter. For an arbitrary PS-ultrafilter ϕ on a countable group G, we construct a mapping f: G → ω such that f(ϕ) is a P-point in the space ω*. We determine a new class of subselective ultrafilters, which is considerably wider than the class of PS-ultrafilters.
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Protasov, I.V. Ultrafilters and Decompositions of Abelian Groups. Ukrainian Mathematical Journal 53, 99–107 (2001). https://doi.org/10.1023/A:1010445018738
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DOI: https://doi.org/10.1023/A:1010445018738