@article{MZM_2000_68_4_a15,
     author = {Yu. A. Aminov},
     title = {On a problem of {Hopf}},
     journal = {Matemati\v{c}eskie zametki},
     pages = {637--640},
     publisher = {mathdoc},
     volume = {68},
     number = {4},
     year = {2000},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_2000_68_4_a15/}
}