首页 | 本学科首页   官方微博 | 高级检索  
     检索      


The projective -character bounds the order of a -base
Authors:Istvá  n Juhá  sz  Zoltá  n Szentmikló  ssy
Institution:Alfréd Rényi Institute of Mathematics, Hungarian Academy of Sciences, POB 127, Budapest, H-1364 Hungary ; Department of Analysis, Eötvös Loránt University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
Abstract:All spaces below are Tychonov. We define the projective $ \pi$- character $ p\,\pi\chi(X)$ of a space $ X$ as the supremum of the values $ \pi\chi(Y)$ where $ Y$ ranges over all (Tychonov) continuous images of $ X$. Our main result says that every space $ X$ has a $ \pi$-base whose order is $ \le p\,\pi\chi(X)$; that is, every point in $ X$ is contained in at most $ p\,\pi\chi(X)$-many members of the $ \pi$-base. Since $ p\,\pi\chi(X) \le t(X)$ for compact $ X$, this is a significant generalization of a celebrated result of Shapirovskii.

Keywords:Projective $\pi $-character  order of a $\pi $-base  irreducible map
点击此处可从《Proceedings of the American Mathematical Society》浏览原始摘要信息
点击此处可从《Proceedings of the American Mathematical Society》下载免费的PDF全文
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号