@article{SF_1987__36_134904,
     author = {E. Spiegel},
     title = {On the uniqueness of the coefficient ring in a semigroup ring.},
     journal = {Semigroup forum},
     pages = {315--322},
     publisher = {mathdoc},
     volume = {36},
     year = {1987},
     zbl = {0658.20041},
     url = {http://geodesic.mathdoc.fr/item/SF_1987__36_134904/}
}