1. M. Anshel andJ. R. Clay, Planar algebraic systems: Some geometric interpretations,J. of Alg.,10 (1968), 166–173.
2. E. Artin,Theory of Algebraic Numbers, Lecture Notes from Mathematisches Institut, Göttingen, Germany.
3. J. R. Clay, The near-rings on groups of low order,Math. Zeitschr.,104 (1968), 364–371.
4. G. Ferrero, Stems Planari e BIB-Disegni,Riv. Mat. Univ. Parma 11 (1970), 1–18.
5. L. Fuchs,Abelian Groups. Pergamon, (New York, 1960).