@article{MS2_1981__48_166739,
     author = {E. Nummelin},
     title = {The convergence of sums of transition probabilities of a positive recurrent {Markov} chain.},
     journal = {Mathematica Scandinavica},
     pages = {79--95},
     publisher = {mathdoc},
     volume = {48},
     year = {1981},
     zbl = {0477.60060},
     url = {http://geodesic.mathdoc.fr/item/MS2_1981__48_166739/}
}