@article{SF_1976__12_134163,
     author = {G. Kowol and H. Mitsch},
     title = {Polynomial functions over commutative semigroups.},
     journal = {Semigroup forum},
     pages = {109--118},
     year = {1976},
     volume = {12},
     zbl = {0338.20089},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__12_134163/}
}