Mathematics – General Topology
Scientific paper
2011-07-07
Mathematics
General Topology
v. 2: added some results, some remarks, various minor improvements. 7 pages. v. 1: 4 pages
Scientific paper
We prove that, for an arbitrary topological space $X$, the following two conditions are equivalent: (a) Every open cover of $X$ has a finite subset with dense union (b) $X$ is $D$-pseudocompact, for every ultrafilter $D$. Locally, our result asserts that if $X$ is weakly initially $\lambda$-compact, and $2^ \mu \leq \lambda $, then $X$ is $D$-\brfrt pseudocompact, for every ultrafilter $D$ over any set of cardinality $ \leq \mu$. As a consequence, if $2^ \mu \leq \lambda $, then the product of any family of weakly initially $\lambda$-compact spaces is weakly initially $\mu$-compact.
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