@article{CTGDC_1977__18_4_431_0,
     author = {Ehresmann, Charles and Ehresmann, Andr\'ee},
     title = {D\'ej\`a vingt ans ...},
     journal = {Cahiers de topologie et g\'eom\'etrie diff\'erentielle},
     pages = {431--432},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {18},
     number = {4},
     year = {1977},
     language = {fr},
     url = {http://www.numdam.org/item/CTGDC_1977__18_4_431_0/}
}