@article{MM2_1970__3_154017,
     author = {J\"urgen Herzog},
     title = {Generators and relations of {Abelian} semigroups and semigroup rings.},
     journal = {Manuscripta mathematica},
     pages = {175--194},
     publisher = {mathdoc},
     volume = {3},
     year = {1970},
     zbl = {0211.33801},
     url = {http://geodesic.mathdoc.fr/item/MM2_1970__3_154017/}
}