@article{MZM_1979_25_3_a8,
     author = {M. O. Otelbaev},
     title = {Estimates of $s$-numbers and completeness conditions for systems of root vectors of non-self-adjoint {Sturm--Liouville} operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {409--418},
     publisher = {mathdoc},
     volume = {25},
     number = {3},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1979_25_3_a8/}
}