anchor.diff:  ;;; Gray Streams classes.
   
   (defclass fundamental-stream (stream standard-object)
  -  ()
  +  ((%openp :initform t))
     (:documentation "The base class for all Gray streams."))
   
   (defclass fundamental-input-stream (fundamental-stream)
  
positive.code:    :close
     :stream-file-position
     :stream-file-length
     ;; Input stream methods.
     :stream-clear-input
     :stream-read-sequence
  
negative.code: 
  (defgeneric stream-element-type (stream))
  (defgeneric close (stream &key abort))
  (defgeneric open-stream-p (stream))
  (defgeneric input-stream-p (stream))
  (defgeneric output-stream-p (stream))
  (defgeneric stream-file-position (stream &optional position-spec))
  (defgeneric stream-file-length (stream))
  (defgeneric stream-clear-input (stream))
  