@article{MZ_1967__98_170746,
     author = {M. M\"uller and A. Lupas},
     title = {Approximationseigenschaften der {Gammaoperatoren.}},
     journal = {Mathematische Zeitschrift},
     pages = {208--226},
     publisher = {mathdoc},
     volume = {98},
     year = {1967},
     zbl = {0171.02301},
     url = {http://geodesic.mathdoc.fr/item/MZ_1967__98_170746/}
}