Volume 22 • Number 2 • 1999   • Cyclic Subgroup Separability of Certain HNN Extensions Wong Peng Choon and Gan Hui Woan Abstract. In this note, we shall show that certain HNN extensions of cyclic subgroup separable groups and certain HNN extensions of subgroup separable groups are cyclic subgroup separable. We also show that one-relator groups with non-trivial centre are cyclic subgroup separable. Full text: PDF