code: def _unique_ordered_lines(line_numbers):
          
  
          if len(line_numbers) == 0:
              return []
  
          # Ensure lines are unique by putting them in a set
          line_set = set(line_numbers)
  
          # Retrieve the list from the set, sort it, and return
          return sorted([line for line in line_set])
docs: Given a list of line numbers, return a list in which each line
          number is included once and the lines are ordered sequentially.