@article{JRAM_1966__223_150753,
     author = {Allen R. Freedman},
     title = {A density inequality for the sum of two sets of lattice points.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {138--141},
     publisher = {mathdoc},
     volume = {223},
     year = {1966},
     zbl = {0139.27303},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1966__223_150753/}
}