@article{CTGDC_2004__45_1_35_0,
     author = {Dawson, R. J. M. and Pare, R. and Pronk, D. A.},
     title = {Free extensions of double categories},
     journal = {Cahiers de Topologie et G\'eom\'etrie Diff\'erentielle Cat\'egoriques},
     pages = {35--80},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {45},
     number = {1},
     year = {2004},
     mrnumber = {2040662},
     zbl = {1055.18001},
     language = {en},
     url = {http://www.numdam.org/item/CTGDC_2004__45_1_35_0/}
}