Example 2 : We give an example of a PDA M that accepts the set of balanced strings of parentheses [] by empty stack. The PDA M is given below.
where 
is defined as
Informally, whenever it sees a [, it will push the ] onto the stack. (first two transitions), and whenever it sees a ] and the top of the stack symbol is [, it will pop the symbol [ off the stack. (The third transition). The fourth transition is used when the input is exhausted in order to pop z off the stack ( to empty the stack) and accept. Note that there is only one state and no final state.