func (it *Iterator) SeekFirst() {
	it.prev = it.s.head
	it.curr, _ = it.s.head.getNext(0)
	it.valid = true
}
func (it *Iterator) SeekFirst() {
	it.prev = it.s.head
	it.curr, _ = it.s.head.getNext(0)
	it.valid = true
}
// SeekFirst moves cursor to the start