@incollection{AST_1980__74__7_0,
     author = {Gerl, Peter},
     title = {A ratio limit theorem},
     booktitle = {Journ\'ees sur les marches al\'eatoires},
     series = {Ast\'erisque},
     pages = {7--14},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {74},
     year = {1980},
     mrnumber = {588154},
     zbl = {0446.60008},
     language = {en},
     url = {http://www.numdam.org/item/AST_1980__74__7_0/}
}