What action is performed by the Turing machine described below?
A) It replaces any string of consecutive 1s to the left of an * with 0s.
B) It leaves the tape unchanged.
C) It places an * at the left end of any string of consecutive 1s appearing to the left of an *.
D) It complements the string of 0s and 1s appearing to the left of an *.

Question

What action is performed by the Turing machine described below? 
A) It replaces any string of consecutive 1s to the left of an * with 0s. 
B) It leaves the tape unchanged. 
C) It places an * at the left end of any string of consecutive 1s appearing to the left of an *. 
D) It complements the string of 0s and 1s appearing to the left of an *.

Quizplus · Accepted Answer

The symbols before the first underscore represent an input string on the tape, which is not provided in the question. The symbols after the second underscore represent the current state of the Turing machine (TB2708_00) and are not relevant to determining the action performed by the machine.

Looking at the part of the machine description before the first underscore, we see that the machine is looking for strings of consecutive 1s to the left of an asterisk symbol (*). When it finds such a string, it places an asterisk to the left of it, but leaves the 1s unchanged. Therefore, choice C, "It places an * at the left end of any string of consecutive 1s appearing to the left of an *," best describes the action performed by this Turing machine.

What Action Is Performed by the Turing Machine Described Below