@article{SM_2006_197_10_a4,
     author = {N. B. Kerimov and Z. S. Aliyev},
     title = {Basis properties of a spectral
},
     journal = {Sbornik. Mathematics},
     pages = {1467--1487},
     publisher = {mathdoc},
     volume = {197},
     number = {10},
     year = {2006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2006_197_10_a4/}
}