private Tree<String> getBestKnownParse(List<String> tags, List<String> words) {
      Tree<String> knownTree = knownParses.getCounter(tags).argMax();
      int wordIndex = 0;
      for (Tree<String> child : knownTree.getPreOrderTraversal()) {
    	 if (child.isLeaf()) child.setLabel(words.get(wordIndex++));
      }
      return knownTree;
    }