pages.append(None)
pages.extend(second_list)
else:
pages.extend(sorted(list(first.union(current))))
if len(current.intersection(last)) == 0:
second_list = sorted(list(last))
pages.append(None)
pages.extend(second_list)
else:
pages.extend(sorted(list(first.union(current))))
if len(current.intersection(last)) == 0:
second_list = sorted(list(last))