  Given a Probabilistic Finite Automata (PFA), a set of states S, and an error
threshold e > 0, our algorithm approximates the infimum probability
(quantifying over all infinite words) that the automata reaches S. Our result
contrasts with the known result that the approximation problem is undecidable
if we consider the supremum instead of the infimum. Since we study the
probability of reaching a set of states, instead of the probability of ending
in an accepting state, our work is more related to model checking than to
formal languages.
