 The first, referred to here as seq2seq, is the standard RNN-based neural machine translation system with attention BIBREF0 . This baseline does not use the parsed data. The multi-source systems improve strongly over both baselines, with improvements of up to 1.5 BLEU over the seq2seq baseline and up to 1.1 BLEU over the parse2seq baseline. 
 Question: Whas is the performance drop of their model when there is no parsed input?
 improvements of up to 1.5 BLEU over the seq2seq baseline