For Hausdorff spaces, $H$-closed = $D$-pseudocompact for all ultrafilters $D$

Paolo Lipparini

Published 2011-07-07, updated 2011-10-22Version 2

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.