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A Turing Machine (TM) is a mathematical model which consists of an infinite length tape divided into cells on which input is given. It consists of a head which reads the input tape. A state register stores the state of the Turing machine.

A Turing machine with left reset is similar to an ordinary Turing machine, but the transition function has the form:

$未:Q脳螕鈫�Q脳螕脳\{鈫�leftarrow\}.$

The difference is that 鈥渓eft arrow鈥� takes the head back to the first square, in one move. So, the head can either move one square to the right, with 鈥溾啋鈥�, or return all the way to the beginning of the tape with 鈥渓eft arrow鈥�. That is,

$未(q,a)=(p,b,leftarrow)$

Means that from state q and symbol a, we go to state is overwritten with b, and the head moves all the way back to the first square of the tape.A Turing machine with left reset is similar to an ordinary Turing machine, but the transition function has the form

$未:Q脳螕脳\{R,RESET\}$

If $未(q,a)=(r,b,RESET),$when the machine is in state q reading an the machine鈥檚 head jumps to the left-hand end of the tape after it writes on the tape and enters state Note that these machines do not have the usual ability to move the head one symbol left