anchor.diff:              (encode-modified list)))) ;p11
               
   ;;; p13
  +
   (defun encode-direct (list)
     "Run-length encoding of a list (direct solution).
   Implement the so-called run-length encoding data compression method directly. I.e. don't explicitly create the sublists containing the duplicates, as in problem P09, but only count them. As in problem P11, simplify the result list by replacing the singleton lists (1 X) by X.
  
positive.code:           (pack list))) ;p09
            
  ;;; p11
  (defun encode-modified (list)
    "Modified run-length encoding.
  Modify the result of problem P10 in such a way that if an element has no duplicates it is simply copied into the result list. 
  
negative.code:       (when list (list list))))
  
  ;;; p10
  
  (defun encode (list)
    "Run-length encoding of a list.
  Use the result of problem P09 to implement the so-called run-length encoding data compression method. 
  