@article{NSJOM_1998_28_1a_6,
     author = {J. U\v{s}an},
     title = {On 

 congruence classes of n-groups},
     journal = {Novi Sad Journal of Mathematics},
     pages = {75-89},
     publisher = {mathdoc},
     volume = {28},
     number = {1},
     year = {1998},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1998_28_1a_6/}
}