@article{IM_1967__4_141892,
     author = {A. PFISTER},
     title = {Zur {Darstellung} definiter {Funktionen} als {Summe} von {Quadraten.}},
     journal = {Inventiones mathematicae},
     pages = {229--237},
     publisher = {mathdoc},
     volume = {4},
     year = {1967},
     zbl = {0222.10022},
     url = {http://geodesic.mathdoc.fr/item/IM_1967__4_141892/}
}