@article{DM_2007_19_4_a9,
     author = {D. M. Motin},
     title = {On identical transformations in commutative semigroups},
     journal = {Diskretnaya Matematika},
     pages = {139--149},
     year = {2007},
     volume = {19},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_2007_19_4_a9/}
}