@article{CMH_1961__35_139201,
     author = {Israel Berstein},
     title = {Homotopy mod. {C} of {Spaces} of {Category} 2.},
     journal = {Commentarii mathematici Helvetici},
     pages = {9--14},
     publisher = {mathdoc},
     volume = {35},
     year = {1961},
     zbl = {0095.16901},
     url = {http://geodesic.mathdoc.fr/item/CMH_1961__35_139201/}
}