Bulletin of the
Korean Mathematical Society BKMS

We show that certain polygonal products of any four groups, amalgamating central subgroups with trivial intersections, have Property E. Using this result, we derive that outer automorphism groups of polygonal products of four polycyclic-by-finite groups, amalgamating central subgroups with trivial intersections, are residually finite.

Keywords: polygonal products of groups, generalized free products, residually finite, conjugacy separable, outer automorphism groups

MSC numbers: Primary 20E26, 20E06; Secondary 20F34, 57M05