Upper neighbours of Čech closure operators

Abstract

Abstract Here, we investigate the existence of upper neighbours in the lattice of $$T_{1}$$ T1 Čech closure operators on a fixed set. In this paper, we prove that a first countable $$T_{1}$$ T1 closure operator has no upper neighbour in the lattice of Čech closure operators.

Keywords

• 54A05
• 03G10