The moves satisfying the conditions given in the definition. As the PDA reads the first half of the input, it remains in the start state q₀and pushes the input symbols on the stock. When it reads the symbol it changes the state from q₀ to q₁without changing the stock. On state q₁ it simply matches input symbols with the stock symbols and erases in case of a match. That is, the symbol The moves satisfying the conditions given in the definition. As the PDA reads the first half of the input, it remains in the start state q₀ and pushes the input symbols on the stock. When it reads the symbol , it changes the state from q₀ to q₁ without changing the stock. On state q₁ it simply matches input symbols with the stock symbols and erases in case of a match. That is, the symbol in tells the m/c when to start looking for Once the input is extended, then the symbol z₀ on stock indicates a proper match for the input to be and hence it accepts by entering state q₂, which is a final state.

Example : Consider the language In this case there is no way to determine when to start comparison because of absence of the symbol in the middle/ The PDA in this case has to guess nondeterministically when the middle symbol comes in the input.

DPDA s and FAs: DCFL s and Regular languages

Equivalence of DFA & NFA proves that non determination does not add power in case of FA s. But it is not true in case of PDA s, i.e., it can be shown that nondeterministic PDA s are more