When the parse forests of the unlabeled data are the union of the outputs of GParser and ZPar, denoted as "Unlabeled ← Z+G", each word has 1.053 candidate heads on English and 1.136 on Chinese, and the oracle accuracy is higher than using 1-best outputs of single parsers (94.97% vs. 92.85% on English, 86.66% vs. 82.46% on Chinese).
we find that although the parser significantly outperforms the supervised GParser on English, it does not gain significant improvement over co-training with ZPar ("Unlabeled ← Z") on both English and Chinese.