@article{SF_1987__36_134901,
     author = {L. Pol\'ak},
     title = {On varieties of completely regular semigroups {II.}},
     journal = {Semigroup forum},
     pages = {253--284},
     year = {1987},
     volume = {36},
     zbl = {0638.20032},
     url = {http://geodesic.mathdoc.fr/item/SF_1987__36_134901/}
}