@article{GDZPPN002219298, title = {Symmetric Semigroups of Integers Generated by 4 Elements.}, journal = {Manuscripta mathematica}, volume = {17}, year = {1975}, pages = {205-220}, zbl = {0317.10061}, url = {http://dml.mathdoc.fr/item/GDZPPN002219298} }
Bresinsky, H. Symmetric Semigroups of Integers Generated by 4 Elements.. Manuscripta mathematica, Tome 17 (1975) pp. 205-220. http://gdmltest.u-ga.fr/item/GDZPPN002219298/