ON THE CARDINALITY OF URYSOHN SPACES AND WEAKLY H-CLOSED SPACES

被引：1
|
作者：
Basile, Fortunata Aurora [1 ]
Carlson, Nathan [2 ]
机构：
[1] Univ Messina, Piazza Pugliatti 1, I-98122 Messina, Italy
[2] Calif Lutheran Univ, Dept Math, 60 W Olsen Rd, Thousand Oaks, CA 91360 USA
来源：
MATHEMATICA BOHEMICA | 2019年 / 144卷 / 03期
关键词：
Urysohn space; theta-closure; pseudocharacter; almost Lindelof degree; cardinality; cardinal invariant;
D O I：
10.21136/MB.2018.0037-18
中图分类号：
O1 [数学];
学科分类号：
0701 ; 070101 ;
摘要：
We introduce the cardinal invariant theta-aL'(X), related to theta-aL(X), and show that if X is Urysohn, then vertical bar X vertical bar <= 2(theta-aL'(x))(chi(X)). As theta-aL'(X) <= aL(X), this represents an improvement of the Bella-Cammaroto inequality. We also introduce the classes of firmly Urysohn spaces, related to Urysohn spaces, strongly semiregular spaces, related to semiregular spaces, and weakly H-closed spaces, related to H-closed spaces.
引用
收藏
页码：325 / 336
页数：12
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