In which categories are first-order axiomatizable hulls characterizable by ultraproducts ?
Cahiers de Topologie et Géométrie Différentielle Catégoriques, Volume 24 (1983) no. 2, p. 215-222
@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 Cat\'egoriques},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {24},
     number = {2},
     year = {1983},
     pages = {215-222},
     zbl = {0519.18003},
     mrnumber = {710042},
     language = {en},
     url = {http://www.numdam.org/item/CTGDC_1983__24_2_215_0}
}
Hien, Bui Huy; Sain, I. In which categories are first-order axiomatizable hulls characterizable by ultraproducts ?. Cahiers de Topologie et Géométrie Différentielle Catégoriques, Volume 24 (1983) no. 2, pp. 215-222. http://www.numdam.org/item/CTGDC_1983__24_2_215_0/

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