This is a PDA from the lecture slides I'm using:
They say it accepts all words that contain double a's. While it makes some sense it's not full proof.
What prevents the second a to be read in the left branch not the right? Or even a 3rd..4th a and so on? Is that the case of human Intervention like needed in PDA for oddpalindrome?
Also as far as I understand a PDA needs to read the whole input tape AND have an empty stack by the end which doesnt seem to be the case if the input is more than an a. What am I not understanding?