@article{IVM_1982_11_a11,
     author = {T. A. Martynova},
     title = {A groupoid of varieties of semigroups with zero},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {77--79},
     year = {1982},
     number = {11},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1982_11_a11/}
}