@article{MZM_1988_43_1_a7,
     author = {V. M. Koltyzhenkov},
     title = {Nonregular variational equations along quasiperiodic solutions of {Hamiltonian} systems},
     journal = {Matemati\v{c}eskie zametki},
     pages = {62--70},
     year = {1988},
     volume = {43},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1988_43_1_a7/}
}