@article{AM2_1974__11_136452,
     author = {O. Marrero},
     title = {Modular {Difference} {Sets.}},
     journal = {Aequationes mathematicae},
     pages = {143--153},
     publisher = {mathdoc},
     volume = {11},
     year = {1974},
     zbl = {0294.05008},
     url = {http://geodesic.mathdoc.fr/item/AM2_1974__11_136452/}
}