@article{CHEB_2012_13_2_a15,
     author = {V. E. Firstov},
     title = {Periodic semi-groups in the ring of residue classes},
     journal = {\v{C}eby\v{s}evskij sbornik},
     pages = {124--130},
     publisher = {mathdoc},
     volume = {13},
     number = {2},
     year = {2012},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/CHEB_2012_13_2_a15/}
}