@article{SF_1972__4_133877,
     author = {J.T. Borrego and E.E. Devun},
     title = {Maximal semigroup orbits.},
     journal = {Semigroup forum},
     pages = {61--68},
     publisher = {mathdoc},
     volume = {4},
     year = {1972},
     zbl = {0253.22001},
     url = {http://geodesic.mathdoc.fr/item/SF_1972__4_133877/}
}