@article{SF_1987__36_134906,
     author = {R. Thron and D. Kittler},
     title = {On semigroups with least generating sets.},
     journal = {Semigroup forum},
     pages = {341--350},
     publisher = {mathdoc},
     volume = {36},
     year = {1987},
     zbl = {0648.20059},
     url = {http://geodesic.mathdoc.fr/item/SF_1987__36_134906/}
}