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