skl/skl.go
func (s *Iterator) Prev() {
	y.AssertTrue(s.Valid())
	s.n, _ = s.list.findNear(s.Key(), true, false) // find <. No equality allowed.
}
func (s *Iterator) Prev() {
	y.AssertTrue(s.Valid())
	s.n, _ = s.list.findNear(s.Key(), true, false) // find <. No equality allowed.
}
// Prev advances to the previous position.