@article{MZ_1977__154_172510,
     author = {Helmut H. Schaefer},
     title = {On the {o-Spectrum} of {Order} {Bounded} {Operators.}},
     journal = {Mathematische Zeitschrift},
     pages = {79--84},
     publisher = {mathdoc},
     volume = {154},
     year = {1977},
     zbl = {0335.47023},
     url = {http://geodesic.mathdoc.fr/item/MZ_1977__154_172510/}
}