@article{SVFU_2023_30_1_a2,
     author = {V. Sh. Roitenberg},
     title = {On second-order differential equations on the circle with the rst degree of structural instability},
     journal = {Matemati\v{c}eskie zametki SVFU},
     pages = {40--50},
     year = {2023},
     volume = {30},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SVFU_2023_30_1_a2/}
}