Can someone please describe how such a machine would work?
Move the head full on the left. Scan the input to verify no # symbol exists. Add # at the end of input. Move the head full on the left. Move one position on the right.
σ and replace it with
σ'. Then go right to the 1st empty char and replace it with
σ. Then go left till you found the 1st
' char. Remove the
' from that char. Move one position the the right and repeat.
When you do that for all characters stop.