Power of Pushdown Machines

Question

Which is more powerful :- 2-way Non-Deterministic Pushdown Machine(NDPDM) or 2-way Deterministic Pushdown Machine(DPDM) ? (or) Do both machine models have the same power ?

Answer 1

DFA and NFA both have same powers but Non-Deterministic Pushdown Machine is more powerful than Deterministic Pushdown Machine.

For Example -

you cannot make Deterministic Pushdown Machine for this string - $W$$W^{T}$ , you can only create Deterministic Pushdown Machine for this string - $W\#W^{T}$

But you can make Non-Deterministic Pushdown Machine for this string - $W$$W^{T}$

Comments

I am asking about 2-way machines , not 1-way Deterministic and non-Determinitic machines..