1. V. S. Korolyuk, ?Asymptotic behavior of the sojourn time of a semi-Markov process in a subset of states,? Ukrainsk. Matem. Zh.,21, No. 6 (1969).
2. V. S. Korolyuk, L. I. Polishchuk, and A. A. Tomusyak, ?On a limit theorem for semi-Markov processes,? Kibernetika, No. 4 (1969).
3. D. V. Gusak and V. S. Korolyuk, ?Asymptotic behavior of semi-Markov processes with a splittable state set,? in: Probability Theory and Mathematical Statistics, No. 5 [in Russian], Izd. KGU, Kiev (1971).
4. A. F. Turbin and L. I. Polishchuk, ?On one case of convergence of a semi-Markov process to a nonstandard Markov chain,? in: Theory of Random Processes, No. 2 [in Russian], Kiev (1973).
5. V. V. Anisimov, ?Limit theorems for sums of random variables given on a subset of states of a Markov process up to the instant of going into a series circuit,? in: Probability Theory and Mathematical Statistics, No. 4 [in Russian], Kiev (1971).