@article{SF_1980__20_134405,
     author = {S. Subbiah and K.D. jr. Magill},
     title = {Another semigroup characterization of the simple closed curve.},
     journal = {Semigroup forum},
     pages = {89--90},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0437.54029},
     url = {http://geodesic.mathdoc.fr/item/SF_1980__20_134405/}
}