public int lastIndexOfFourth(M m, int index) {
   try {
     for (int i = index; i >= 0; i--) {
       if ((m == null ? get(i).fourth == null : m.equals(get(i).fourth))) return i;
     }
   } catch (final Exception e) {
   }
   return -1;
 }
 public synchronized boolean removeFifth(M m) {
   Quint<T, K, L, M, N> pair;
   for (final Iterator<Quint<T, K, L, M, N>> i = iterator(); i.hasNext(); ) {
     pair = i.next();
     if ((m == null ? pair.fifth == null : m.equals(pair.fifth))) {
       i.remove();
       return true;
     }
   }
   return false;
 }
 public boolean containsFifth(M m) {
   for (final Iterator<Quint<T, K, L, M, N>> i = iterator(); i.hasNext(); ) {
     if ((m == null) ? i.next() == null : m.equals(i.next().fifth)) return true;
   }
   return false;
 }