@article{SF_1989__39_2_134971,
     author = {L.M. Shneerson},
     title = {On the axiomatic rank of varieties generated by a semigroup or monoid with one defining relation.},
     journal = {Semigroup forum},
     pages = {17--38},
     publisher = {mathdoc},
     volume = {39},
     number = {2},
     year = {1989},
     zbl = {0671.20056},
     url = {http://geodesic.mathdoc.fr/item/SF_1989__39_2_134971/}
}