A theorem due to Tweedie (1974), showing the existence and uniqueness of an $R$-invariant measure for $R$-recurrent Markov chains, is derived by an alternative and direct method.
"A Direct Construction of the $R$-Invariant Measure for a Markov Chain on a General State Space." Ann. Probab. 4 (4) 674 - 679, August, 1976. https://doi.org/10.1214/aop/1176996037