@article{CMJ_1999__49_4_a2,
     author = {Tunca, G\"ulen Ba\c{s}canbaz and Bairamov, Elgiz},
     title = {Discrete spectrum and principal functions of non-selfadjoint differential operator},
     journal = {Czechoslovak Mathematical Journal},
     pages = {689--700},
     publisher = {mathdoc},
     volume = {49},
     number = {4},
     year = {1999},
     mrnumber = {1746697},
     zbl = {1015.34073},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMJ_1999__49_4_a2/}
}