2. 2
Ex
A 2-tape Turing machine that checks for
palindromes
1. Copies the input from tape 1 to tape 2
2. Positions head 1 at the beginning of the string in tape 1
and head 2 at the end of the string in tape 2
3. Moves the two heads in opposite directions checking that
the two symbols are identical and erasing the copy in
tape 2 at the same time
3.
4. Construct a two-tape Turing machine with
input alphabet {a, b, c} that accepts the
language {ai
bi
ci
| i ≥ 0}.
4
6. Construct a two-tape Turing machine that
accepts strings in which each a is followed
by an increasing number of b’s; that is, the
strings are of the form
abn1
abn2
・ ・ ・ abnk
, k > 0,
where n1 < n2 < ・ ・ ・ < nk
6
