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Even Covers and Collectionwise Normal Spaces

  • H. L. Shapiro (a1) and F. A. Smith (a2)

Extract

The concept of an even cover is introduced early in elementary topology courses and is known to be valuable. Among other facts it is known that X is paracompact if and only if every open cover of X is even. In this paper we introduce the concept of an n-even cover and show its usefulness. Using n-even we define an embedding that on closed subsets is equivalent to collectionwise normal. We also give sufficient conditions for a point finite open cover to have a locally finite refinement and also sufficient conditions for this refinement to be even. Finally we show that the collection of all neighborhoods of the diagonal of X is a uniformity if and only if every even cover is normal. This last result is particularly interesting in light of the fact that every normal open cover is even.

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Copyright

References

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1. Alo, R. A. and Shapiro, H. L., Normal topological spaces (Cambridge University Press, Cambridge, Great Britain, 1974).
2. Bing, R. H., Metrization of topological spaces, Can. J. Math. 3 (1951), 175186.
3. Cohen, H. J., Sur un problème de M. Dieudonné, C. R. Acad. Sci. Paris 234 (1952), 290292.
4. Egorov, V. I., On the metric dimension of point sets, Mat. Sb. 48 (1959), 227250. (Russian)
5. Hayashi, Y., On countably metacompact spaces, Bull. Univ. Prefecture Ser. A, 8 (1959/60), 161164.
6. Isbell, J. R., Uniform spaces (Amer. Math. Soc, Providence, 1964).
7. Michael, E., Point-finite and locally finite coverings, Can. J. Math. 7 (1955), 275279.
8. Smith, J. C., Jr., Characterizations of metric-dependent dimension functions, Proc. Amer. Math. Soc. 19 (1968), 12641269.
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Even Covers and Collectionwise Normal Spaces

  • H. L. Shapiro (a1) and F. A. Smith (a2)

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