@article{SF_1981__23_134508,
     author = {E.A. Behrens},
     title = {Semigroups with a noncommutative arithmetic.},
     journal = {Semigroup forum},
     pages = {95--118},
     publisher = {mathdoc},
     volume = {23},
     year = {1981},
     zbl = {0472.06025},
     url = {http://geodesic.mathdoc.fr/item/SF_1981__23_134508/}
}