@article{SF_1976__13_134214,
     author = {T. Nordahl},
     title = {Periodic weakly-cancellative semigroups.},
     journal = {Semigroup forum},
     pages = {219--220},
     year = {1976},
     volume = {13},
     zbl = {0369.20038},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__13_134214/}
}