@article{SF_1974__7_134005,
     author = {Mario Petrich},
     title = {All subvarieties of a certain variety of semigroups.},
     journal = {Semigroup forum},
     pages = {104--152},
     publisher = {mathdoc},
     volume = {7},
     year = {1974},
     zbl = {0282.20048},
     url = {http://geodesic.mathdoc.fr/item/SF_1974__7_134005/}
}