## 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

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