For an infinite set , a closed under finite unions family with , and any , the topology on is investigated to give answers to the following open problem in various models of or : Is there a non-empty Hausdorff, crowded zero-dimensional -space in the absence of the axiom of choice? Spaces of the form for and are of special importance here. Among many other results, the following theorems are proved in : (1) If is uncountable, then is a crowded zero-dimensional Hausdorff space, and if is also quasi Dedekind-finite, then is a -space; (2) is a -space if and only if is regular; (3) the axiom of countable choice for families of finite sets is equivalent to the statement for every infinite Dedekind-finite set $X$, $\mathbf{S}(X,[X]^{\leqω})$ is a $P$-space''; (4) the statement admits a topology such that is a crowded, zero-dimensional Hausdorff -space’’ is strictly weaker than the axiom of countable choice for families of subsets of ; (5) the statement there exists a non-empty, well-orderable crowded zero-dimensional Hausdorff $P$-space'' is strictly weaker than is regular’'. A lot of relevant independence results are obtained.

生成讲解博客的中文版本

生成AI智能校验的中文版本