anchor.diff:  (defmethod print-object ((obj trigger) stream)
     (if (and (slot-boundp obj 'pattern)
              (slot-boundp obj 'process))
  -    (format stream "(trigger ~a ~a)" (pattern obj) (process obj))
  +    (format stream "(trigger ~s ~s)" (pattern obj) (process obj))
       (call-next-method)))
   
   (defun trigger (pattern process)
  
positive.code:   (if (and (slot-boundp obj 'name)
             (slot-boundp obj 'process)
             (slot-boundp obj 'continuation))
      (format stream "{~a~:[ ~a~:[ ~a~;~]~;~]}"
              (name obj)
              (and (eql (process obj) null-process)
                   (eql (continuation obj) null-process))
  
negative.code:     by a more local variable with the same name."))
  
  (defmethod print-object ((obj process-variable) stream)
    (format stream "?~s" (name obj)))
  
  (defun process-variable (name)
    (make-instance 'process-variable :name name))
  