@article{SF_1974__9_134082,
     author = {H. J\"urgensen},
     title = {Fastideale von {Halbgruppen.}},
     journal = {Semigroup forum},
     pages = {261--270},
     publisher = {mathdoc},
     volume = {9},
     year = {1974},
     url = {http://geodesic.mathdoc.fr/item/SF_1974__9_134082/}
}