@article{10_4153_CMB_1969_081_4,
     author = {Marica, J. and Sch\"oheim, J.},
     title = {Differences of {Sets} and {A} {Problem} of {Graham}},
     journal = {Canadian mathematical bulletin},
     pages = {635--637},
     year = {1969},
     volume = {12},
     number = {5},
     doi = {10.4153/CMB-1969-081-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1969-081-4/}
}