# Recognize end of Input in a Turing Machine

If I have a turing machime TM, can I recognize end of input on the tape?

I know that the "end of input" in a turing machine is signaled with a special character, $\sqcup$.

Can I do this -

Let $TM$ be a turing machine.

Until we reach the first $\sqcup$, continue. If we reached $\sqcup$, replace it with a special character - #.

Is it "legal" to that this?

• Thank you! In that sense, can I make a reduction for $EQ_{TM}$ problem with that sense? Let's say I assume that $EQ_{LBA}$ is decidable, can I find the end of input in $EQ_{TM}$, run $EQ_{LBA}$ and "decide" $EQ_{TM}$? In that method, I prove that $EQ_{LBA}$ is undecidable. @Yuval Filmus – Alan Jul 6 '18 at 13:45