List<CorefMention[]> allMentions = sample.getMentions();
List<Parse> allParses = sample.getParses();
for (int si = 0; si < allMentions.size(); si++) {
CorefMention mentions[] = allMentions.get(si);
Parse p = allParses.get(si);
for (Mention extent : mentionFinder.getMentions(new DefaultParse(p, si))) {
if (extent.getParse() == null) {
// not sure how to get head index