Visibly Pushdown Transducers with Look-Ahead
Abstract
Visibly Pushdown Transducers (VPTs) form a subclass of pushdown transducers. In this paper, we investigate the extension of VPTs with look-ahead (VPTs+LA). Intuitively they are VPTs that can check that the well-nested subword starting at the current position belongs to a given visibly pushdown language. First, we show that VPTs+LA are not more expressive than VPTs, but they are exponentially more succinct. Second, we show that the class of deterministic VPTs+LA corresponds exactly to the class of functional VPTs. Finally, we show that, while VPTs+LA may be exponentially more succinct than VPTs, checking equivalence of functional VPTs+LA is, as for VPTs, Exptime-complete.
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