@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 Cat\'egoriques},
     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://geodesic.mathdoc.fr/item/CTGDC_1976__17_2_113_0/}
}