@article{EUG_1987_14_a2,
     author = {I. Istratescu},
     title = {On some classes of {Operators} on {Hilbert} spaces},
     journal = {E\ensuremath{\upsilon}\ensuremath{\kappa}\ensuremath{\lambda}\ensuremath{\varepsilon}\ensuremath{\acute\iota}\ensuremath{\delta}\ensuremath{\eta}\ensuremath{\varsigma} \ensuremath{\Gamma}},
     pages = {15--18},
     year = {1987},
     volume = {14},
     language = {gr},
     url = {http://geodesic.mathdoc.fr/item/EUG_1987_14_a2/}
}