# Turing Machine that always returns a blank tape

Is it possible to construct a Turing Machine such that given any finite input on a tape $s$, it clears the tape in a finite amount of time?

I have used such a TM as an intermediate step to show a reduction from the State Entry Problem to is $w \in L(M)$ problem but I don't know if it is feasible to construct one.

Even if we assume that the head of the TM always starts at the leftmost character on the tape and keep moving write, clearing each symbol we encounter, if the tape is infinite, how will we know when to stop moving right?

• when the head reaches a special symbol say #. Initially tape of Turing machine is infinite cells each with symbol #. When a finite input is written on tape # denotes end of input. – sashas May 1 '16 at 13:40
• In other words, the input alphabet excludes the special character, so starting at the leftmost character on the tape and moving right, as soon as you see a special character you know you've reached the end of the input – Rick Decker May 1 '16 at 18:11