The INSERT GROUP command inserts one or more groups into one
    or more other groups. Both groups must exist. When you use the
    INSERT GROUP command to insert group A into group B, the elements
    accessible through group B change as the contents of group A
    change. A group cannot be a member of itself; that is, it cannot
    be a subgroup of itself. For example, you cannot insert group A
    into group B if group A already contains group B.