@article{CM_1939__6__428_0,
     author = {Eilenberg, Samuel},
     title = {G\'en\'eralisation du th\'eor\`eme de {M.} {H.} {Hopf} sur les classes des transformations en surfaces sph\'eriques},
     journal = {Compositio Mathematica},
     pages = {428--433},
     publisher = {Johnson Reprint Corporation},
     volume = {6},
     year = {1939},
     zbl = {0022.40902},
     language = {fr},
     url = {http://www.numdam.org/item/CM_1939__6__428_0/}
}