anchor.diff:        (declare (ignore forms))
         (check-type id symbol)
         (check-type args list)
  -      (when-let (keyword (has-lambda-list-keyword-p args))
  -        (error 'ptree-lambda-list-keyword-error
  -               :id id
  -               :keyword keyword))))
  +      (when-let (llks (intersection args lambda-list-keywords))
  +        (error 'ptree-lambda-list-keyword-error :id id :llks llks))))
     (with-gensyms (tree)
       `(let ((,tree (make-ptree)))
          ,@(loop
  
positive.code:                 root
                  (compute-ptree root ptree (check-kernel)))))))))
  
  (defun has-lambda-list-keyword-p (list)
    (some (lambda (elem) (find elem lambda-list-keywords)) list))
  
  (defmacro ptree (defs &body body)
    "Create a ptree using `flet' syntax.
  
  
negative.code:    "Attempted to execute a node which had no function."))
  
  (define-condition ptree-lambda-list-keyword-error (ptree-error)
    ((llks :initarg :llks :reader ptree-error-llks))
    (:report
     (lambda (err stream)
       (format stream
               "Function arguments in `ptree' cannot contain lambda list ~
                keywords.~%In definition of ~a found: ~{~s~^ ~}"
               (ptree-error-id err)
               (ptree-error-llks err))))
    (:documentation
     "Lambda list keywords found in function definition."))
  
  