@article{ELMA_1973__28_141107,
     author = {Konrad Voss},
     title = {In memoriam {Heinz} {Hopf.}},
     journal = {Elemente der Mathematik},
     pages = {81--83},
     publisher = {mathdoc},
     volume = {28},
     year = {1973},
     zbl = {0257.01012},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1973__28_141107/}
}