Transactions of the American Mathematical Society · 2001 · 16 citations · 6 references
Let $u(\kappa )$ be the space of uniform ultrafilters on $\kappa$. If $\kappa$ is regular, then there is an $\mathbf x \in u(\kappa )$ which is not an accumulation point of any subset of $u(\kappa )$ of size $\kappa$ or less. $\mathbf x$ is also good, in the sense of Keisler.
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Some theorems of set theory and their topological consequences
R. Engelking, M. Karłowicz · Fundamenta Mathematicae · 1965 · 115 citations · Full text
H. Jerome Keisler · Annals of Mathematics · 1964 · 81 citations