Show that a Turingmachine with tapes that are infinite in both directions semi-decides the same languages as a classical TM. Apart from the entry-word, the tapes are filled with empty spaces and the head's on the first letter of the entry-word
Under "classical" TM we understand a TM that has a tape that starts at the first letter and is infinite at the right side.
I don't quite understand what to prove here. The only difference between the two TM's is that I can/can't hit the left border of the tape. I could make this scenario a rejected state in the double infinite TM because it can't happen on the single infinite TM.