@article{SF_1971__2_133821,
     author = {T. Head},
     title = {Commutative semigroups having greatest regular images.},
     journal = {Semigroup forum},
     pages = {130--137},
     publisher = {mathdoc},
     volume = {2},
     year = {1971},
     zbl = {0225.20040},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__2_133821/}
}