@article{MZ_1968__105_170972,
     author = {V. Istratescu and I. Istratescu},
     title = {On {Normaloid} {Operators.}},
     journal = {Mathematische Zeitschrift},
     pages = {153--156},
     year = {1968},
     volume = {105},
     zbl = {0159.19403},
     url = {http://geodesic.mathdoc.fr/item/MZ_1968__105_170972/}
}