@article{CTGDC_1976__17_2_113_0, author = {Porter, Timothy}, title = {Abstract homotopy theory in procategories}, journal = {Cahiers de topologie et g\'eom\'etrie diff\'erentielle}, pages = {113--124}, publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS}, volume = {17}, number = {2}, year = {1976}, mrnumber = {445496}, zbl = {0349.18012}, language = {en}, url = {http://archive.numdam.org/item/CTGDC_1976__17_2_113_0/} }