Countable Paracompactness and Weak Normality Properties By

نویسنده

  • JOHN MACK
چکیده

After proving this theorem, we obtain similar results for the topological spaces studied in [7] and [11]. Also, cogent examples are given and the relation this note bears to the work of others is discussed. We shall follow the terminology of [5] except we shall assume separation properties for a space only when these assumptions are explicitly stated. For an infinite cardinal m, a set A in a topological space will be called a Gm-set (respectively, a regular Gm-set) provided it is the intersection of at most m open sets (respectively, at most m closed sets whose interiors contain A). If m = S0, we shall use the familiar terms GVset and regular C-set. It is clear that the zero-set of any continuous real valued function is a regular (/¿-set and that the intersection of no more than in such zero-sets is a regular Cmset. In the remaining part of this paper, we shall use these facts without explicitly mentioning them. Definition. For an infinite cardinal nt, a topological space is m-normal if each pair of disjoint closed sets, one of which is a regular Cm-set, have disjoint neighborhoods. For m = S0, we shall use the more suggestive term 8-normal. Note that a normal space is m-normal and that a regular space is normal if and only if it is m-normal for every infinite cardinal m. On the other hand, a compact Fi-space that is not Hausdorff is m-normal for every infinite cardinal but yet it fails to be normal. Recall that a space is m-paracompact if each open cover having cardinal less than or equal to m has a locally finite open refinement. Characterizations of mparacompact spaces may be found in [14] and [8].

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Monotone versions of δ-normality

According to Mack a space is countably paracompact if and only if its product with [0, 1] is δ-normal, i.e. any two disjoint closed sets, one of which is a regular Gδ-set, can be separated. In studying monotone versions of countable paracompactness, one is naturally led to consider various monotone versions of δ-normality. Such properties are the subject of this paper. We look at how these prop...

متن کامل

Large Cardinals and Small Dowker Spaces

We prove that, if there is a model of set-theory which contains no first countable, locally compact, scattered Dowker spaces, then there is an inner model which contains a measurable cardinal. A Hausdorff space is normal if, for every pair of disjoint closed sets C and D, there is a pair of disjoint open sets, U containing C and V containing D. A (normal) space is binormal if its product with t...

متن کامل

Answering a question on relative countable paracompactness

In [6], Yoshikazu Yasui formulates some results on relative countable paracompactness and poses some questions. Like it is the case with many other topological properties [1], countable paracompactness has several possible relativizations. Thus a subspace Y ⊂ X is called countably 1-paracompact in X provided for every countable open cover U of X there is an open cover V of X which refines U and...

متن کامل

Linearly Ordered Topological Spaces

This work is devoted to the study of certain cardinality modifications of paracompactness and compactness in the setting of linearly ordered spaces. Some of the concepts treated here have previously been studied by Aquaro [l]1, Gulden [4], Kennison [5], Mansfield [6], Morita [7], and Poppe [9]. On the other hand, the concept of m-boundedness, introduced in §2, is new. Our main results (Theorems...

متن کامل

A Note on Complete Collectionwise Normality and Paracompactness

1. A question that has aroused considerable interest and which has remained unanswered is the following. Is a normal Moore space metrizable? Both R. H. Bing and F. B. Jones have important results which go a long way toward answering this question. For example, Bing has proved that a collectionwise normal Moore space is metrizable [l ] while Jones has shown that a separable normal Moore space is...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2010