Trimming Visibly Pushdown Automata

We study the problem of trimming visibly pushdown automata (VPA). We first describe a polynomial time procedure which, given a visibly pushdown automaton that accepts only well-nested words, returns an equivalent visibly pushdown automaton that is trimmed. We then show how this procedure can be lifted to the setting of arbitrary VPA. Furthermore, we present a way of building, given a VPA, an equivalent VPA which is both deterministic and trimmed.