@article{PA_1993_1_a12,
     author = {B. M. Shirokov},
     title = {On a lenght of the continued fraction's period},
     journal = {Problemy analiza},
     pages = {85--90},
     year = {1993},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PA_1993_1_a12/}
}