Guy Fayolle I. A. Ignatyuk V. A. Malyshev M. V. Menshikov Random walks in two-dimensional complexes. 269-300 1991 9 Queueing Syst. 3 http://dx.doi.org/10.1007/BF01158467 db/journals/questa/questa9.html#FayolleIMM91