@article{DE_1989_25_1_a22,
     author = {M. A. Mustafin},
     title = {The {Riesz} basis of the {Bitsadze--Samarski{\v\i}} spectral problem with infinitely multiple eigenvalues},
     journal = {Differencialʹnye uravneni\^a},
     pages = {172--174},
     publisher = {mathdoc},
     volume = {25},
     number = {1},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_1_a22/}
}