1. S. N. Artemov, "Modal logics axiomatizing probability," Izv. Akad. Nauk SSSR, Ser. Mat.,49, No. 6, 1123–1154 (1985).
2. M. L. Minsky, "Recursive unsolvability of Post's problem of ‘Tag’ and topics in theory of Turing machines," Ann. Math.,74, 437–455 (1961).
3. S. Isard, "A finitely axiomatizable undecidable extension of K," Theoria,43, No. 3, 195–202 (1977).
4. A. I. Mal'tsev, Algorithms and Recursive Functions [in Russian], Nauka, Moscow (1986).
5. L. L. Maksimova, "Interpolation in normal modal logics," in: Nonclassical Logics, Mathematical Investigations, No. 98 [in Russian], Kishinev (1987), pp. 40–56.