@article{DM_2016_28_4_a9,
     author = {P. V. Roldugin},
     title = {On the number of subsets of the residue ring such that the difference of any pair of elements is not invertible},
     journal = {Diskretnaya Matematika},
     pages = {122--138},
     publisher = {mathdoc},
     volume = {28},
     number = {4},
     year = {2016},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_2016_28_4_a9/}
}