@article{CMH_1963__38_139275,
     author = {Charles Ehresmann},
     title = {Structures quotient.},
     journal = {Commentarii mathematici Helvetici},
     pages = {219--283},
     publisher = {mathdoc},
     volume = {38},
     year = {1963},
     url = {http://geodesic.mathdoc.fr/item/CMH_1963__38_139275/}
}