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doi:10.1016/0304-3975(94)00111-U 
Copyright © 1995 Published by Elsevier Science B.V.
Regular paper
Deterministic top-down tree transducers with iterated look-ahead
Giora Slutzki and Sándor Vágvölgyi
, 1
Communicated by A. Salomaa
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Abstract
It is known that by iterating the look-ahead tree languages for deterministic top-down tree automata, more and more powerful recognizing devices are obtained. Let DR0 = DR, where DR is the class of all tree languages recognizable by deterministic top-down tree automata, and let, for n 
1, DRn be the class of all tree languages recognizable by deterministic top-down tree automata with DRn−1 look-ahead. Then DR0 
DR1 DR2 …. Slutzki and Vágvölgyi (1993) showed that the composition powers of the class of all deterministic top-down tree transformations with deterministic top-down look-ahead (DTTDR) form a proper hierarchy, i.e. (DTTDR)n (DTTDR)n + 1 for n 0. Along the proof they studied the notion of the deterministic top-down tree transducer with DRn look-ahead (dttDRn) and showed that (DTTDR)n + 1 
DTTDRn (n 0), where DTTDRn stands for the class of all tree transformations induced by dttDRn'S. Our aim is to show the reversed inclusion, i.e. DTTDRn (DTTDR)n + 1 (n 0). This implies a precise characterization DTTDRn = (DTTDR)n + 1 (n 0), and implies that the classes DTTDRn (n 0) form a proper hierarchy.
