@article{TMF_2007_153_1_a5,
     author = {Yu. N. Demkov and P. B. Kurasov},
     title = {Von {Neumann--Wigner} theorem: {Level} repulsion and degenerate eigenvalues},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {68--85},
     publisher = {mathdoc},
     volume = {153},
     number = {1},
     year = {2007},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_2007_153_1_a5/}
}