@article{10_1017_S2040618500034985,
     author = {Halberstam, H. and Laxton, R. R.},
     title = {Perfect difference sets},
     journal = {Glasgow mathematical journal},
     pages = {177--184},
     year = {1964},
     volume = {6},
     number = {4},
     doi = {10.1017/S2040618500034985},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S2040618500034985/}
}