Editing Markov chain (section)

===Time reversal===
For a CTMC ''X''<sub>''t''</sub>, the time-reversed process is defined to be <math> \hat X_t = X_{T-t}</math>. By [[Kelly's lemma]] this process has the same stationary distribution as the forward process.

A chain is said to be ''reversible'' if the reversed process is the same as the forward process. [[Kolmogorov's criterion]] states that the necessary and sufficient condition for a process to be reversible is that the product of transition rates around a closed loop must be the same in both directions.