@article{JRAM_1981__325_152362,
     author = {P. Ribenboim},
     title = {Active sums of groups.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {153--182},
     year = {1981},
     volume = {325},
     zbl = {0451.20028},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1981__325_152362/}
}