@article{SF_1975__10_134120,
     author = {T.E. Hall and D.W.H. Gillam and N.H. Williams},
     title = {An addition theorem for finite semigroups.},
     journal = {Semigroup forum},
     pages = {273--276},
     publisher = {mathdoc},
     volume = {10},
     year = {1975},
     zbl = {0324.20074},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__10_134120/}
}