@article{SF_1995__51_1_135396,
     author = {S. Schwarz},
     title = {Powers of subsets in a finite semigroup.},
     journal = {Semigroup forum},
     pages = {1--22},
     publisher = {mathdoc},
     volume = {51},
     number = {1},
     year = {1995},
     zbl = {0833.20074},
     url = {http://geodesic.mathdoc.fr/item/SF_1995__51_1_135396/}
}