the blank symbol #
* is the initial state
* is the set of accepting (final) states
* is the first probabilistic transition function. is a movement one cell to the left on the Turing machine's tape and is a movement one cell to the right.
* is the second probabilistic transition function.

At each step, the Turing machine probabilistically applies either the transition function or the transition function . This choice is made independently of all prior choices. In this way, the process of selecting a transition