The major reason is that we did not perform any reordering or distorting during decoding with PTT.
in both t2s and s2t systems, the BLEU-4 score benefits of PRS were covered by the composed rules: both PTT+C S 3 and PTT+C 3 performed significant better (p < 0.01) than PTT+PRS, and there are no significant differences when appending PRS to PTT+C 3 .