@article{MZ_1980__172_172964,
     author = {Roland Derndinger},
     title = {\"Uber das {Spektrum} positiver {Generatoren.}},
     journal = {Mathematische Zeitschrift},
     pages = {281--293},
     publisher = {mathdoc},
     volume = {172},
     year = {1980},
     zbl = {0444.47030},
     url = {http://geodesic.mathdoc.fr/item/MZ_1980__172_172964/}
}