@article{CHEB_2021_22_3_a30,
     author = {E. Liflyand},
     title = {Ball's lemma as an exercise},
     journal = {\v{C}eby\v{s}evskij sbornik},
     pages = {464--466},
     publisher = {mathdoc},
     volume = {22},
     number = {3},
     year = {2021},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CHEB_2021_22_3_a30/}
}