A countable Fréchet-Urysohn space of uncountable character
The author constructs an infinite strong completely separable almost disjoint family on \(\omega\) and, by means of that, a countable Fréchet-Urysohn \(\alpha_4\) but not \(\alpha_3\) space all finite powers of which are Fréchet-Urysohn.
Fréchet-Urysohn space (for finite sets, for bounded sets)
(strong completely separable) almost disjoint family
scientific article; zbMATH DE number 5290943
scientific article