@article{CMH_1955__29_139100,
     author = {Heinz Hopf},
     title = {Schlichte {Abbildungen} und lokale {Modifikationen} 4-dimensionaler komplexer {Mannigfaltigkeiten.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {132--156},
     publisher = {mathdoc},
     volume = {29},
     year = {1955},
     zbl = {0064.41703},
     url = {http://geodesic.mathdoc.fr/item/CMH_1955__29_139100/}
}