Topology and its Applications ( IF 0.6 ) Pub Date : 2021-04-08 , DOI: 10.1016/j.topol.2021.107685 Wei-Feng Xuan , Yan-Kui Song
We say that a space X is dually CCC (respectively, weakly Lindelöf, separable) if for any neighbourhood assignment ϕ on X, there is a CCC (respectively, weakly Lindelöf, separable) subspace such that covers X. In this paper, we mainly show that
(1) A dually CCC first countable Hausdorff space has cardinality at most and a dually weakly Lindelöf first countable normal space has cardinality at most .
(2) Let , where is a scattered monotonically normal space for any . If a subspace is dually CCC then and a normal subspace is DCCC if and only if .
(3) Assume . A normal dually CCC space X with has extent at most .
(4) A dually separable Hausdorff space X with a -diagonal has extent at most and a dually separable regular space X with a -diagonal has cardinality at most .
(5) A dually CCC Hausdorff space with a -diagonal has cellularity at most .
中文翻译:
双重CCC空间的基本不变式
我们说一个空间X是双重CCC(分别为弱Lindelof的,可分离)如果任何邻居分配φ在X,有CCC(分别为弱Lindelof的,可分离)子空间 这样 涵盖X。在本文中,我们主要表明
(1)双重CCC的第一个可数Hausdorff空间最多具有基数 Lindelöf的第一个双重弱的第一个可数法向空间最多具有基数 。
(2)让 , 在哪里 是任何物体的分散单调法线空间 。如果是子空间 然后是双重CCC 和一个普通的子空间 是DCCC当且仅当 。
(3)假设 。一个正常的双重CCC空间X与 最多有范围 。
(4)一种双重可分离豪斯多夫空间X与-对角线最多具有范围 和双重可分正则空间X与-对角线最多具有基数 。
(5)具有CCC双重Hausdorff空间 -对角线最多具有细胞性 。