anchor.diff:      access in the way we usually deal with them."))
   
   (defmethod print-object ((obj parallel-composition) stream)
  -  (format stream "(par~{ ~a~})"
  +  (format stream "(par~{ ~s~})"
             (map-parallel-composition #'identity obj)))
   
   (defun parallel-composition (&rest processes)
  
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))
  