@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/} }