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On the free set number of topological spaces and their Gδ-modifications
Topology and its Applications ( IF 0.6 ) Pub Date : 2021-07-19 , DOI: 10.1016/j.topol.2021.107793 István Juhász 1 , Lajos Soukup 1 , Zoltán Szentmiklóssy 2
中文翻译:
在拓扑空间的自由设定数量及其摹δ 2'-修饰
更新日期:2021-07-20
Topology and its Applications ( IF 0.6 ) Pub Date : 2021-07-19 , DOI: 10.1016/j.topol.2021.107793 István Juhász 1 , Lajos Soukup 1 , Zoltán Szentmiklóssy 2
Affiliation
For a topological space X we propose to call a subset free in X if it admits a well-ordering that turns it into a free sequence in X. The well-known cardinal function is then definable as and will be called the free set number of X.
We prove several new inequalities involving and , where is the -modification of X:
- •
if X is and if X is ;
- •
for any -space X;
- •
if X is and if X is .
中文翻译:
在拓扑空间的自由设定数量及其摹δ 2'-修饰
对于拓扑空间X,我们建议将其称为子集 释放的X,如果承认一个良序的是把它变成一个免费的序列X。众所周知的基数函数 然后可以定义为 并称为X的自由集数。
我们证明了几个新的不等式,包括 和 , 在哪里 是个 - 修改X:
- •
如果X是 和 如果X是;
- •
对于任何 -空格X ;
- •
如果X是 和 如果X是.