The Josefson-Nissenzweig theorem and filters on [Formula: see text]
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For a free filter F on ω , endow the space N F = ω ∪ { p F } , where p F ∉ ω , with the topology in which every element of ω is isolated whereas all open neighborhoods of p F are of the form A ∪ { p F } for A ∈... ...
