anchor.diff:  
   (defmethod add-block (environment symbol)
     (make-instance 'block
  +    :next environment
       :name symbol
       :identity (gensym)))
   
  
positive.code: 
  (defmethod add-local-function (environment function-name)
    (make-instance 'function
      :name function-name
      :identity (gensym)))
  
  
negative.code: 
  (defmethod add-tag (environment symbol)
    (make-instance 'tag
      :next environment
      :name symbol
      :identity (gensym)))
  
  