1. Hall, Jr M., Cyclic projective planes, Duke Math. J., 1947, 14: 1079–1090.
2. Menon, P. K., Difference sets in abelian groups, Proc. Amer. Math. Soc., 1960, 11: 368–376.
3. McFarland, R. L., On multipliers of abelian difference sets, Ph.D. Dissertation,Ohio State University, 1970.
4. Qiu, W. S., A method of studying the multiplier conjecture and its applications, Research Report, Institute of Mathematics, Peking University, 1994, 40.
5. Qiu, W. S., A character approach to the multiplier conjecture and a new result for the case n = 3n1, J. Combinatorial Designs, 1997, 5(2): 81–93.