1. Basu A.P. (1971) Bivariate failure rate.-J.Amer.Statist.Assoc., 66, p. 103–104.
2. Buchanan W.B. and Sinpurwalla N.D. (1977) Some stochastic characterizations of multivariate survival.-In: Theory and Applications of Reliability, v. 2, Acad. Press, New York, p. 329–348.
3. Marshall A.W. (1975) Multivariate distributions with monotone hazard rate.-In: Reliability and Fault Tree Analysis, p. 259–284.
4. Rachev S.T. (1977). Reliability of ageing systems.-Annuaire Univ. Sofia, Fac.Math.Méc., v. 68 (1973/74), p. 339–347.
5. Rachev S.T. (1978). Theorems of moments and their applications for NBU distributions.-In: Proceedings of the Fourth Spring Conference of Bulgarian Mathematical Society, Pernik, April 1975, p. 303–310.