iterator.go
func (it *Iterator) Prev() {
	prev := it.list.getPrev(it.nd, 0)
	it.setNode(prev, true)
}
func (it *Iterator) Prev() {
	prev := it.list.getPrev(it.nd, 0)
	it.setNode(prev, true)
}
func ( it * Iterator ) Prev ( ) { prev := it . list . getPrev ( it . nd , 0 ) it . setNode ( prev , true ) }
// Prev moves to the previous position. If there are no previous nodes, then
// Valid() will be false after this call.
Prev moves to the previous position . If there are no previous nodes then Valid () will be false after this call .