Shu-Hao Sun, Koo-Guan Choo
New properties of the concentric circle space and its applications to cardinal inequalities

Comment.Math.Univ.Carolinae 32,2 (1991) 395-403.

Abstract:It is well-known that the concentric circle space has no $G_\delta $-diagonal nor any countable point-separating open cover. In this paper, we reveal two new properties of the concentric circle space, which are the weak versions of $G_\delta $-diagonal and countable point-separating open cover. Then we introduce two new cardinal functions and sharpen some known cardinal inequalities.

Keywords: concentric circle space, weak $G_\delta $-diagonal, point-separating -open cover, cardinal function
AMS Subject Classification: 54G05, 54A25