Affiliation:
1. Freelance author , Hsinchu County , Taiwan
Abstract
Abstract
Given any regular
T
0
{T_{0}}
(equivalently, regular
T
1
{T_{1}}
) space X, the question of whether X being Lindelöf implies X being a D-space is an active open problem.
This article gives a class of handy examples of a second countable collectionwise normal collectionwise Hausdorff
T
0
{T_{0}}
space of uncountable cardinal,
with at most countably many singletons being not closed,
that is not a D-space.
Also given is a class of handy examples of a second countable hyperconnected
T
0
{T_{0}}
space of uncountable cardinal,
with at most countably many singletons being not closed,
that is not a D-space.
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