1. The structure and order of the group of central automorphisms of a finite group;Hughes, N. J. S.;Proc. London Math. Soc. (2),1951
2. A. Kuroš, Teoriia Grupp, Moscow-Leningrad, 1944.
3. H. Zassenhaus, Gruppentheorie, Leipzig-Berlin, 1937. (References are to the 1949 English translation.)