code: public static <T> Iterator<T> reorderIf( RandSeq randSeq, Iterator<T> sequence)
      {
      return randSeq==null? sequence : randSeq.reorder( sequence);
      }
docs: Applies the given <code>randSeq</code> to rearrange the given sequence in a random order.
  If <code>randSeq</code> is <code>null</code>, returns the sequence unchanged.