Berkovich, Yakov and Zvonimir Janko. "§75. Elements of order ≤ in p-groups" Volume 2. Berlin, Boston: Walter de Gruyter, 2008. 277-281. Web. Retrieved 23 May. 2013, from http://www.degruyter.com/view/books/9783110208238/9783110208238.277/9783110208238.277.xml

Berkovich, Y. & Janko, Z. (2008). §75. Elements of order ≤ in p-groups. Volume 2 (pp. 277-281). Berlin, Boston: Walter de Gruyter. Retrieved 23 May. 2013, from http://www.degruyter.com/view/books/9783110208238/9783110208238.277/9783110208238.277.xml

Berkovich, Yakov and Zvonimir Janko. 2008. §75. Elements of order ≤ in p-groups. In Volume 2, 277-281. Berlin, Boston: Walter de Gruyter. Retrieved 23 May. 2013, from http://www.degruyter.com/view/books/9783110208238/9783110208238.277/9783110208238.277.xml