2 citations to https://www.mathnet.ru/rus/mzm2197

1. E. A. Kudryavtseva, A. A. Oshemkov, “Structurally Stable Nondegenerate Singularities of Integrable Systems”, Russ. J. Math. Phys., 29:1 (2022), 57  
2. K. Efstathiou, D. A. Sadovskií, “Normalization and global analysis of perturbations of the hydrogen atom”, Rev. Mod. Phys., 82:3 (2010), 2099