@article{AL_1988_27_4_a4,
     author = {M. V. Sapir},
     title = {Algorithmic problems in varieties of semigroups},
     journal = {Algebra i logika},
     pages = {440--463},
     year = {1988},
     volume = {27},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1988_27_4_a4/}
}