@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 = {archive.numdam.org/item/CM_1939__6__428_0/} }
Eilenberg, Samuel. Généralisation du théorème de M. H. Hopf sur les classes des transformations en surfaces sphériques. Compositio Mathematica, Tome 6 (1939) , pp. 428-433. http://archive.numdam.org/item/CM_1939__6__428_0/