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

页码：325 / 336

页数：12

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