@article{SF_1995__50_3_135380,
     author = {D.C. Jackson},
     title = {Direct products of cyclic semigroups and unions of groups.},
     journal = {Semigroup forum},
     pages = {223--232},
     publisher = {mathdoc},
     volume = {50},
     number = {3},
     year = {1995},
     zbl = {0828.20048},
     url = {http://geodesic.mathdoc.fr/item/SF_1995__50_3_135380/}
}