@article{MAN_1967__172_161580,
     author = {Gerd Wittstock},
     title = {\"Uber invariante {Teilr\"aume} zu positiven {Trasformationen} in {R\"aumen} mit indefiniter {Metrik}},
     journal = {Mathematische Annalen},
     pages = {167--175},
     publisher = {mathdoc},
     volume = {172},
     year = {1967},
     zbl = {0149.34903},
     url = {http://geodesic.mathdoc.fr/item/MAN_1967__172_161580/}
}