@article{MV_1975_27_4_a3,
     author = {W. Hahn},
     title = {\"Uber orthogonalit\"atserhaltende {Operatoren}},
     journal = {Matemati\v{c}ki vesnik},
     pages = {337 },
     year = {1975},
     volume = {27},
     number = {4},
     url = {http://geodesic.mathdoc.fr/item/MV_1975_27_4_a3/}
}