Le and Zuidema (2014)'s reranker is an exception among supervised parsers because it employs an extremely expressive model whose features are ∞order 2 .
it is worth noting that, in this case, each phase with iterated reranking could be seen as an approximation of hard-EM (see Equation 2) where the first step is replaced by instead of searching over the treebank space, the search is limited in a neighbour set N(D i ) generated by k-best parser P i .