no. 2
In which categories are first-order axiomatizable hulls characterizable by ultraproducts ?
Cahiers de topologie et géométrie différentielle, Tome 24 (1983) no. 2, pp. 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},
     pages = {215--222},
     year = {1983},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {24},
     number = {2},
     mrnumber = {710042},
     zbl = {0519.18003},
     language = {en},
     url = {https://www.numdam.org/item/CTGDC_1983__24_2_215_0/}
}
TY  - JOUR
AU  - Hien, Bui Huy
AU  - Sain, I.
TI  - In which categories are first-order axiomatizable hulls characterizable by ultraproducts ?
JO  - Cahiers de topologie et géométrie différentielle
PY  - 1983
SP  - 215
EP  - 222
VL  - 24
IS  - 2
PB  - Dunod éditeur, publié avec le concours du CNRS
UR  - https://www.numdam.org/item/CTGDC_1983__24_2_215_0/
LA  - en
ID  - CTGDC_1983__24_2_215_0
ER  - 
%0 Journal Article
%A Hien, Bui Huy
%A Sain, I.
%T In which categories are first-order axiomatizable hulls characterizable by ultraproducts ?
%J Cahiers de topologie et géométrie différentielle
%D 1983
%P 215-222
%V 24
%N 2
%I Dunod éditeur, publié avec le concours du CNRS
%U https://www.numdam.org/item/CTGDC_1983__24_2_215_0/
%G en
%F 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, Tome 24 (1983) no. 2, pp. 215-222. https://www.numdam.org/item/CTGDC_1983__24_2_215_0/

1 Andreka, H. & Nemeti, I., os L emma holds in every category, Studia Sci. Math. Hungar. 13 (1978), 361- 376. | Zbl | MR

2 Andr Eka, H. & Nemeti, I., Formulas and ultraproducts in categories, Beitrage z ur Algebra und G eome tri e 8 (1979), 13 3-151. | Zbl | MR

3 Henkin, L., Monk, J.D., Tarski, A., Andreka, H. & Nemeti, I., Cylindric set algebras, Lecture Notes in Math. 883, Springer (1981). | Zbl | MR

4 Herrlich, H. & Strecker, G.E., Category Theory, Allyn & Bacon, 1973. | Zbl | MR

5 Hien, B.H., & Sain, I., Elementary classes in the injective subcategories approach to abstract model theory, Preprint 15 / 1982 Math. Inst. Hun g. A cad. Sc. Budapest. Part of this is to appear in Periddica Math. Hungar. | Zbl | MR

6 Nemeti, I., Connections between cylindric algebras and initial algebra semantics of CF languages, Colloq. Math. Soc. Bolyai 26, North Holland (1981), 561. | Zbl

7 Nemeti, I. & Sain, I., Cone implicational subcategories and some Birkhoff type theorems, Colloq. Math. Soc. Bolyai 29, North Holland (1981), 535-578. | Zbl | MR

8 Fakir, J.& Haddad, L., Objets cohérents et ultraproduits dans les catégories, J. of Algebra 21- 3 (1972). | Zbl | MR

9 Guitart, R. & Lair, C., Calcul syntaxique des modèles et calcul des for-mules internes, Diagrammes 4 (1980). | Zbl | MR | Numdam

10 Andreka, H. & Ne Meti, L., Injectivity in categories to represent all first order formulas, Demonstratio. Math. 12 (1979), 717-732. | Zbl | MR

11 Hien, B.H., Nemeti, I. & Sain, I., Category theoretic notions of ultraproducts, Preprint 19/ 1982, Math. Inst. Acad. Sc., Budapest. Part of this is to appear in Studia Math. Sc. Hungar. | MR