@article{IVM_1981_3_a14,
     author = {L. M. Martynov},
     title = {The groupoid of prevarieties of semigroups with a~zero},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {80--81},
     publisher = {mathdoc},
     number = {3},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1981_3_a14/}
}