@article{SF_1985__31_134748,
     author = {I. Levi},
     title = {On the set of ranges of a transformation semigroup.},
     journal = {Semigroup forum},
     pages = {219--226},
     publisher = {mathdoc},
     volume = {31},
     year = {1985},
     zbl = {0549.20049},
     url = {http://geodesic.mathdoc.fr/item/SF_1985__31_134748/}
}