pushdown automata (pda)

Another ExampleConsider the set L = {ww R : w ∈ {a,b} + }.The idea for an npda to accept L is to guess the middleof the input string and matches the front substring andthe rear substring. The front substring is pushed intothe stack, and the rear substring is matched againstthe stack content (in the reverse order).Specifically, we construct an npdaM = ({q 0 ,q 1 ,q 2 }, {a,b}, {a,b,z},δ,q 0 ,z, {q 2 }),where state q 0 signals that the input position is in thefront part, and state q 1 signals that the input position isin the rear.Pushdown Automata – p. 9