@article{AL_1975_14_3_a1,
     author = {Yu. L. Ershov},
     title = {The upper semilattice of numerations of a finite set},
     journal = {Algebra i logika},
     pages = {258--284},
     publisher = {mathdoc},
     volume = {14},
     number = {3},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1975_14_3_a1/}
}