@article{CMH_1940__13_138770,
     author = {Heinz Hopf},
     title = {Ein topologischer {Beitrag} zur reellen {Algebra.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {219--239},
     publisher = {mathdoc},
     volume = {13},
     year = {1940},
     zbl = {0024.36002},
     url = {http://geodesic.mathdoc.fr/item/CMH_1940__13_138770/}
}