@article{SF_1977__14_186357,
     author = {H. J\"urgensen and P. Wick},
     title = {Die {Halbgruppen} der {Ordnungen} = <7 .},
     journal = {Semigroup forum},
     pages = {69--80},
     publisher = {mathdoc},
     volume = {14},
     year = {1977},
     zbl = {0363.20050},
     url = {http://geodesic.mathdoc.fr/item/SF_1977__14_186357/}
}