<math>t\sim t^{'}\equiv \overleftarrow{s_{t^{'}}}\sim \overleftarrow{s_t} \triangleq Pr(\overrightarrow{s}|\overleftarrow{s_t} )=Pr(\overrightarrow{s} |\overleftarrow{s_{t^{'}}} )</math>, | <math>t\sim t^{'}\equiv \overleftarrow{s_{t^{'}}}\sim \overleftarrow{s_t} \triangleq Pr(\overrightarrow{s}|\overleftarrow{s_t} )=Pr(\overrightarrow{s} |\overleftarrow{s_{t^{'}}} )</math>, |