@article{MZM_1981_30_4_a7,
     author = {G. M. Gubreev and A. I. Kovalenko},
     title = {Tests for completeness of root subspaces of a differentiation operator with abstract boundary conditions},
     journal = {Matemati\v{c}eskie zametki},
     pages = {543--552},
     publisher = {mathdoc},
     volume = {30},
     number = {4},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1981_30_4_a7/}
}