@article{MM2_1979__29_154669,
     author = {Wilhelm Singhof},
     title = {Minimal {Coverings} of {Manifolds} with {Balls.}},
     journal = {Manuscripta mathematica},
     pages = {385--416},
     publisher = {mathdoc},
     volume = {29},
     year = {1979},
     zbl = {0415.55001},
     url = {http://geodesic.mathdoc.fr/item/MM2_1979__29_154669/}
}