@article{10_4153_CJM_1968_124_2,
     author = {Johnsen, E. C.},
     title = {Special {Abelian} {Group} {Difference} {Sets}},
     journal = {Canadian journal of mathematics},
     pages = {1269--1275},
     year = {1968},
     volume = {20},
     number = {1},
     doi = {10.4153/CJM-1968-124-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1968-124-2/}
}