@article{SF_1984__29_134693,
     author = {S. Armstrong},
     title = {The structure of type {A} semigroups.},
     journal = {Semigroup forum},
     pages = {319--336},
     publisher = {mathdoc},
     volume = {29},
     year = {1984},
     zbl = {0546.20057},
     url = {http://geodesic.mathdoc.fr/item/SF_1984__29_134693/}
}