anchor.diff:        (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. 
  
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:       list))
        
  ;;; p09
  
  (defun pack (list)
    "Pack consecutive duplicates of list elements into sublists.
  If a list contains repeated elements they should be placed in separate sublists.
  