Abstract
Practice running and constructing PDAs.
Review the Pushdown Automata section of the Tutorial.
When you create a new PDA, JFlap give you an option to allow multiple or single (only) character input.
Our definition of PDAs (from the textbook) allows only single input characters, but allows multiple symbols to be pushed onto the stack in one transition.
To get this in JFlap, select “Multiple Character Input” but remember that you must only transition on one input character at a time.
Here is the PDA for $0^n1^n$.
Try executing it (“Input -> Step by Closure”) on these inputs:
Here is the PDA for $ww^R$.
Try executing it (“Input -> Step by Closure”) on these inputs:
A palindrome is a string that reads the same backwards as forwards. All strings in our $ww^R$ language are palindromes. But “1001001” is also a palindrome, and is not in $ww^R$.
Can you modify the $ww^R$ PDA so that it recognizes all palindromes over $\{0, 1\}^*$? (This is a good way to see if you have really embraced thinking about non-determinism.)