1. Baumslag, Gilbert: Some aspects of groups with unique roots. To appear in Acta Math. (Stockh.).
2. Baumslag, Gilbert: Wreath products andp-groups. Proc. Cambridge Phil. Soc.55, 224?231 (1959).
3. Baumslag, Gilbert: Roots and wreath products. To appear in Proc. Cambridge Phil. Soc.56, 109?117 (1960).
4. Hall, P.: Finiteness conditions for soluble groups. Proc. London Math. Soc. (3)4, 419?436 (1954).
5. Kaloujnine, L., andM. Krasner: Produit complet des groupes de permutations et probl�me d'extension des groupes. Acta Sci. Math. Szeged13, 208?230 (1950);14, 36?66, 69?82 (1951).