On Generalized Free Products of Residually Finitep-Groups

We derive necessary and sufficient conditions for generalized free products of free groups or finitely generated torsion-free nilpotent groups, amalgamating a cycle, to be residually finitep-groups. Using this, we characterize the residually finitep-group property of tree products of finitely generated torsion-free nilpotent groups amalgamating cycles.