Given the following pushdown automaton, transform it into a context-free grammar.

(0, a, a, pop, 0)

(0, b, b, pop, 0)

(0, Epsilon, S, pop, 0)

(0, Epsilon, S, [pop, push(a), push(S), push(a)], 0)

(0, Epsilon, S, [pop, push(b), push(S), push(a)], 0)

Or, instead, you can use the following pushdown automaton to do the transformation. (Lambdas are used instead of Epsilons in the image. They are equivalent.)