1. W. Hanf, “The boolean algebra of logic,” Bull. Am. Math. Soc., 20, No. 4, 456-502 (1975).
2. S. Lempp, M. Peretyat’kin, and R. Solomon, “The Lindenbaum algebra of the theory of the class of all finite models,” J. Math. Log., 2, No. 2, 145-225 (2002).
3. V. L. Selivanov, “Universal Boolean algebras with applications,” Abstr. Int. Conf. Algebra, Novosibirsk (1991), p. 127.
4. V. L. Selivanov, Hierarchies, Numerations, Index Sets, Handwritten notes (1992).
5. V. L. Selivanov, “Positive structures,” in Computability and Models, Perspectives East and West, S. B. Cooper and S. S. Goncharov (eds.), Kluwer Academic/Plenum Publishers, New York (2003), pp. 321-350.