@article{MZ_1962__79_170082,
     author = {Helmut H. Schaefer},
     title = {\"Uber die {Additivit\"at} von {Spektralma{\ss}en.}},
     journal = {Mathematische Zeitschrift},
     pages = {456--459},
     publisher = {mathdoc},
     volume = {79},
     year = {1962},
     zbl = {0102.10601},
     url = {http://geodesic.mathdoc.fr/item/MZ_1962__79_170082/}
}