Volume 31 • Number 1 • 2008   • Subgroup Separability and Conjugacy Separability of Certain HNN Extensions P. C. Wong and K. B. Wong Abstract. In this note, we give characterizations for certain HNN extensions of polycyclic-by-finite groups with central associated subgroups to be subgroup separable and conjugacy separable. We shall do this by showing the equivalence of subgroup separability and conjugacy separability in this type of HNN extensions. 2000 Mathematics Subject Classification: Primary 20E06, 20E26; Secondary 20F10, 20F19. Full text: PDF