1. A. T. Nurtazin, “Countable infinite existentially closed models of universally axiomatizable theories,” Sib. Adv. Math., 26, No. 2, 99-125 (2016).
2. P. J. Cohen, Set Theory and the Continuum Hypothesis, W. A. Benjamin, New York (1966).
3. J. Barwise and A. Robinson, “Completing theories by forcing,” Ann. Math. Log., 2, 119-142 (1970).
4. R. Fraïssé, “Sur quelques classifications des systèmes de rélations,” Publ. Sci. Univ. Alger, Sér. A, 1, 35-182 (1955).
5. Handbook of Mathematical Logic, Vol. 1, Model Theory, J. Barwise (ed.), North-Holland, Amsterdam (1977).