@article{CTGDC_1982__23_3_269_0,
     author = {Wong, Y. L.},
     title = {Chain homotopy pullbacks and pushouts},
     journal = {Cahiers de topologie et g\'eom\'etrie diff\'erentielle},
     pages = {269--278},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {23},
     number = {3},
     year = {1982},
     mrnumber = {675338},
     zbl = {0503.55014},
     language = {en},
     url = {http://www.numdam.org/item/CTGDC_1982__23_3_269_0/}
}