@article{MZM_1971_9_2_a4,
     author = {I. N. Astaf'eva and V. I. Malovikov},
     title = {Second solutions of equations involving positive operators in degenerate cases},
     journal = {Matemati\v{c}eskie zametki},
     pages = {143--149},
     publisher = {mathdoc},
     volume = {9},
     number = {2},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1971_9_2_a4/}
}