@article{ELMA_1974__29_141140,
     author = {O. Baier and W. Vinzenz},
     title = {Der },
     journal = {Elemente der Mathematik},
     pages = {81--84},
     publisher = {mathdoc},
     volume = {29},
     year = {1974},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1974__29_141140/}
}