@article{MV_1975_27_1_a2,
     author = {Gh. Constantin},
     title = {On operators with the same spectrum},
     journal = {Matemati\v{c}ki vesnik},
     pages = {25 },
     publisher = {mathdoc},
     volume = {27},
     number = {1},
     year = {1975},
     url = {http://geodesic.mathdoc.fr/item/MV_1975_27_1_a2/}
}