anchor.diff:          (message (setf (process kell) null-process))
           (parallel-composition (setf (messages (process kell))
                                       (delete process (messages (process kell))))
  -                              (case (length (map-parallel-composition #'identity
  -                                                                      (process kell)))
  +                              (case (length (map-parallel-composition
  +                                             #'identity
  +                                             (process kell)))
                                   (0 (setf (process kell) null-process))
  -                                (1 (setf (process kell) (car (map-parallel-composition #'identity
  -                                                                                          (process kell))))))))
  -      (error "The (message) process ~a is not contained in ~a, and thus can not be removed."
  +                                (1 (setf (process kell)
  +                                         (car (map-parallel-composition
  +                                               #'identity
  +                                               (process kell))))))))
  +      (error "The (message) process ~a is not contained in ~a, and thus can ~
  +              not be removed."
                process (process kell))))
     (:method ((process kell) kell)
       (if (find process (kells-in (process kell)))
  
positive.code:         (trigger (setf (process kell) null-process))
          (parallel-composition (setf (triggers (process kell))
                                      (delete process (triggers (process kell))))
                                (case (length (map-parallel-composition #'identity
                                                                        (process kell)))
                                  (0 (setf (process kell) null-process))
                                  (1 (setf (process kell) (car (map-parallel-composition #'identity
                                                                                            (process kell))))))))
        (error "The (trigger) process ~a is not contained in ~a, and thus can not be removed."
               process (process kell))))
    (:method (process kell)
      (if (find process (primitives-in (process kell)))
  
negative.code: 
  (defgeneric compose-processes (process-a process-b)
    (:documentation
     "Conses up a new parallel composition that contains both process-a and
      process-b.")
    (:method (process-a process-b)
      (let ((pc (make-instance 'parallel-composition)))
        (compose-processes (compose-processes pc process-a)
  