An amalgamation theorem for group extensions (Q1068199)

A number of amalgamation theorems of the following form are proved. Let G, H be groups, each containing a group A as a normal subgroup. Then there is a group B, generated by subgroups isomorphic to G and H, with \(G\cap H=A\), and satisfying a number of additional properties. In each case the group B is constructed explicitly as the amalgamated free product \(G*_ AH\) modulo some suitable normal subgroup N.