@article{FPM_2006_12_7_a15,
     author = {R. G. Smirnov},
     title = {The classical {Bertrand{\textendash}Darboux} problem},
     journal = {Fundamentalʹna\^a i prikladna\^a matematika},
     pages = {231--250},
     year = {2006},
     volume = {12},
     number = {7},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FPM_2006_12_7_a15/}
}