@article{CTGDC_1983__24_2_215_0,
     author = {Hien, Bui Huy and Sain, I.},
     title = {In which categories are first-order axiomatizable hulls characterizable by ultraproducts ?},
     journal = {Cahiers de topologie et g\'eom\'etrie diff\'erentielle},
     pages = {215--222},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {24},
     number = {2},
     year = {1983},
     mrnumber = {710042},
     zbl = {0519.18003},
     language = {en},
     url = {http://www.numdam.org/item/CTGDC_1983__24_2_215_0/}
}