@article{MZ_1968__106_171015,
     author = {C.R. Putnam},
     title = {Hyponormal {Operators} and {Low} {Density} {Spectra.}},
     journal = {Mathematische Zeitschrift},
     pages = {167--169},
     publisher = {mathdoc},
     volume = {106},
     year = {1968},
     zbl = {0157.45503},
     url = {http://geodesic.mathdoc.fr/item/MZ_1968__106_171015/}
}