code: func (sl *SkipList) GetWithPosition(cmp common.Comparator) (common.Comparator, uint64) {
  	n, pos := sl.search(cmp, nil, nil)
  	if n == nil {
  		return nil, 0
  	}
  
  	return n.entry, pos - 1
  }
docs: // GetWithPosition will retrieve the value with the provided key and
  // return the position of that value within the list.  Returns nil, 0
  // if an associated value could not be found.