anchor.diff:    object)
   
   (defmethod scale-name ((this symbol))
  -  (scale-name (scale this)))
  +  (when this
  +    (scale-name (scale this))))
   
   (defmethod scale-notes ((this symbol))
  -  (scale-notes (scale this)))
  +  (when this
  +    (scale-notes (scale this))))
   
   (defmethod scale-tuning ((this symbol))
     (when this
  
positive.code:   object)
  
  (defmethod tuning-name ((this symbol))
    (tuning-name (tuning this)))
  
  (defmethod tuning-pitches ((this symbol))
    (tuning-pitches (tuning this)))
  
  (defmethod tuning-octave-ratio ((this symbol))
    (tuning-octave-ratio (tuning this)))
  
  ;;; Scala (.scl) scale file support
  ;; http://www.huygens-fokker.org/scala/scl_format.html
  
negative.code:   object)
  
  (defmethod chord-name ((this symbol))
    (when this
      (chord-name (chord this))))
  
  (defmethod chord-scale ((this symbol))
    (when this
      (chord-scale (chord this))))
  
  (defmethod chord-indexes ((this symbol))
    (when this
      (chord-indexes (chord this))))
  
  (defmethod describe-object ((chord chord) stream)
    (with-slots (name scale) chord
  