1. Lecture Notes in Mathematics;C. D. H. Cooper,1974
2. G. Higman and B. H. Neumann,Groups as groupoids with one law, Publ. Math. Debrecen2 (1951–2), 215–221.
3. A. Hulanicki and S. Świerczkowski,On group operations other than xy or yx, Publ. Math. Debrecen9 (1962), 142–148.
4. B. Huppert,Endliche Gruppen I, inErgebnisse der Mathematik und ihrer Grenzgebiete, Band37, Springer-Verlag, Berlin, Heidelberg and New York, 1967.
5. Avinoam Mann,Regular p-groups, Israel J. Math.10 (1971), 471–477.