@article{MZM_1999_66_1_a3,
     author = {V. A. Bykovskii},
     title = {Vahlen theorem for two-dimensional convergents},
     journal = {Matemati\v{c}eskie zametki},
     pages = {30--37},
     publisher = {mathdoc},
     volume = {66},
     number = {1},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1999_66_1_a3/}
}