Variations on known and recent cardinality bounds
Abstract
Sapirovskii [18] proved that , for a regular space . We introduce the -pseudocharacter of a Urysohn space , denoted by , and prove that the previous inequality holds for Urysohn spaces replacing the bounds on celluarity and on pseudocharacter with a bound on Urysohn cellularity (which is a weaker conditon because ) and on -pseudocharacter respectivly (note that in general and in the class of regular spaces ). Further, in [6] the authors generalized the Dissanayake and Willard's inequality: , for Hausdorff spaces [25], in the class of -Hausdorff spaces and de Groot's result: , for Hausdorff spaces [11], in the class of spaces (see Theorems 2.22 and 2.23 in [6]). In this paper we restate Theorem 2.22 in [6] in the class of -Urysohn spaces and give a variation of Theorem 2.23 in [6] using new cardinal functions, denoted by , , , , and . In [5] the authors introduced the Hausdorff point separating weight of a space denoted by and proved a Hausdorff version of Charlesworth's inequality [7]. In this paper, we introduce the Urysohn point separating weight of a space , denoted by , and prove that , for a Urysohn space .
Cite
@article{arxiv.1709.10497,
title = {Variations on known and recent cardinality bounds},
author = {Fortunata Aurora Basile and Maddalena Bonanzinga and Nathan Carlson},
journal= {arXiv preprint arXiv:1709.10497},
year = {2017}
}
Comments
14 pages