@article{SF_1984__28_134641,
     author = {B.M. Castellano},
     title = {Monoids on the 2-disk.},
     journal = {Semigroup forum},
     pages = {83--92},
     publisher = {mathdoc},
     volume = {28},
     year = {1984},
     zbl = {0531.22001},
     url = {http://geodesic.mathdoc.fr/item/SF_1984__28_134641/}
}