1. J. Wolfowitz, Strong converse of the coding theorem for indecomposable channels, Sankhya (1963). See also the abstract by the same title in Ann. Math. Statist. 33 (1962), 1212.
2. Weak ergodicity in non-homogeneous Markov chains;Hajnal, J.;Proc. Cambridge Philos. Soc.,1958
3. Inhomogeneous Markov chains;Sarymsakov, T. A.;Teor. Verojatnost. i Primenen,1961