func (s *Iterator) SeekToFirst() {
	s.n = s.list.getNext(s.list.head, 0)
}
func (s *Iterator) SeekToFirst() {
	s.n = s.list.getNext(s.list.head, 0)
}
// SeekToFirst seeks position at the first entry in list.
// Final state of iterator is Valid() iff list is not empty.