Geodesic
AB-compacta
Commentationes Mathematicae Universitatis Carolinae, Tome 49 (2008) no. 1, pp. 141-146 Cet article a éte moissonné depuis la source Czech Digital Mathematics Library

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We define a compactum $X$ to be AB-compact if the {\it cofinality\/} of the character $\chi(x,Y)$ is countable whenever $x\in Y$ and $Y\subset X$. It is a natural open question if every AB-compactum is necessarily first countable. We strengthen several results from [Arhangel'skii and Buzyakova, {\it Convergence in compacta and linear Lindelöfness\/}, Comment. Math. Univ. Carolin. {\bf 39} (1998), no. 1, 159--166] by proving the following results. \roster \item Every AB-compactum is countably tight. \item If $\frak p = \frak c$ then every AB-compactum is Fr\`echet-Urysohn. \item If $\frak c \aleph_\omega$ then every AB-compactum is first countable. \item The cardinality of any AB-compactum is at most $2^{ \frak c}$. \endroster
We define a compactum $X$ to be AB-compact if the {\it cofinality\/} of the character $\chi(x,Y)$ is countable whenever $x\in Y$ and $Y\subset X$. It is a natural open question if every AB-compactum is necessarily first countable. We strengthen several results from [Arhangel'skii and Buzyakova, {\it Convergence in compacta and linear Lindelöfness\/}, Comment. Math. Univ. Carolin. {\bf 39} (1998), no. 1, 159--166] by proving the following results. \roster \item Every AB-compactum is countably tight. \item If $\frak p = \frak c$ then every AB-compactum is Fr\`echet-Urysohn. \item If $\frak c \aleph_\omega$ then every AB-compactum is first countable. \item The cardinality of any AB-compactum is at most $2^{ \frak c}$. \endroster
Classification : 03E65, 54A20, 54A25, 54A35, 54D30
Keywords: compact space; first countable space; character of a point 
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Gorelic, Isaac; Juhász, István. AB-compacta. Commentationes Mathematicae Universitatis Carolinae, Tome 49 (2008) no. 1, pp. 141-146. http://geodesic.mathdoc.fr/item/CMUC_2008_49_1_a12/