private void findNext() {
    if (iter1 == null || iter2 == null) {
      next0 = null;
      return;
    }
    T next1 = null;
    T next2 = null;
    while (true) {
      if (next1 == null) {
        if (! iter1.hasNext()) {
          iter1 = null;
          next0 = null;
          return;
        }
        next1 = iter1.next();
      }
      if (next2 == null) {
        if (! iter2.hasNext()) {
          iter2 = null;
          next0 = null;
          return;
        }
        next2 = iter2.next();
      }
      int c = next1.compareTo(next2);
      if (c == 0) {
        next0 = next1;
        return;
      }
      else if (c < 0) {
        next1 = null;
        continue;
      }
      else {
        next2 = null;
        continue;
      }
    }
  }