Peter G. Harrison Ting Ting Lee Separable equilibrium state probabilities via time reversal in Markovian process algebra. 161-182 2005 346 Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.tcs.2005.08.007 db/journals/tcs/tcs346.html#HarrisonL05