1. G. Cantor, Beträge zur Begrundung der transfiniten Mengenlehre, Math. Ann. 46 (1895), 481-512.
2. C. C. Chang, A lemma on ultraproducts and some applications, Notices Amer. Math. Soc. 7 (1960), 635.
3. \bysame, Theory of models of infinite valued logic. I, II, III and IV, Notices Amer. Math. Soc. 8 (1961), 68-69 and 141-142.
4. C. C. Chang and H. J. Keisler, Pairs of cardinals for models of a given theory, Notices Amer. Math. Soc. 8 (1961), 275.
5. On closure under direct product;Chang, C. C.;J. Symbolic Logic,1958