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Cardinal invariants of dually CCC spaces
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 YX such that ϕ(Y)={ϕ(y):yY} covers X. In this paper, we mainly show that

(1) A dually CCC first countable Hausdorff space has cardinality at most 2c and a dually weakly Lindelöf first countable normal space has cardinality at most 2c.

(2) Let Y={Yi:in}, where Yi is a scattered monotonically normal space for any i=0,1,...,n. If a subspace XY is dually CCC then e(X)ω and a normal subspace XY is DCCC if and only if e(X)ω.

(3) Assume 2<c=c. A normal dually CCC space X with χ(X)c has extent at most c.

(4) A dually separable Hausdorff space X with a Gδ-diagonal has extent at most c and a dually separable regular space X with a Gδ-diagonal has cardinality at most c.

(5) A dually CCC Hausdorff space with a Gδ-diagonal has cellularity at most c.



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φX,有CCC(分别为弱Lindelof的,可分离)子空间ÿX 这样 ϕÿ={ϕÿÿÿ}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 2个C 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个C

(2)让 ÿ={ÿ一世一世ñ}, 在哪里 ÿ一世 是任何物体的分散单调法线空间 一世=01个ñ。如果是子空间Xÿ 然后是双重CCC ËXω 和一个普通的子空间 Xÿ 是DCCC当且仅当 ËXω

(3)假设 2个<C=C。一个正常的双重CCC空间XχXC 最多有范围 C

(4)一种双重可分离豪斯多夫空间XGδ-对角线最多具有范围 C和双重可分正则空间XGδ-对角线最多具有基数 C

(5)具有CCC双重Hausdorff空间 Gδ-对角线最多具有细胞性 C

更新日期:2021-04-13
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