@article{10_21136_CPM_1980_118047,
     author = {Svoboda, Karel},
     title = {On characterization of the sphere in $E^4$ by means of the parallelness of certain vector fields},
     journal = {\v{C}asopis pro p\v{e}stov\'an{\'\i} matematiky},
     pages = {56--72},
     publisher = {mathdoc},
     volume = {105},
     number = {1},
     year = {1980},
     doi = {10.21136/CPM.1980.118047},
     mrnumber = {560758},
     zbl = {0435.53004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CPM.1980.118047/}
}