@article{AL_1977_16_4_a3,
     author = {V. M. Kopytov and N. Ya. Medvedev},
     title = {Varieties of lattice-ordered groups},
     journal = {Algebra i logika},
     pages = {417--423},
     publisher = {mathdoc},
     volume = {16},
     number = {4},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1977_16_4_a3/}
}