anchor.diff:  			   :setter-form-maker #'(lambda (value-form)
   						  `(setf (gethash ,entry *bib-entry*)
   						    ,value-form))
  -			   :side-effects (make-instance 'side-effects :used-variables (list entry))
  +			   :side-effects (make-instance 'side-effects :used-variables (list entry)
  +							:variables-used-before-assigned (list entry))
   			   :type func-type
   			   :argument-types '()
   			   :result-types (list type))))
  
positive.code:   lisp-form-maker
    (side-effects null-side-effects)
    setter-form-maker
    ;; For use in the BST interpreter:
    value					; value as a variable
    body
  
negative.code: 			     :lisp-form-maker #'(lambda () lisp-name)
  			     :setter-form-maker #'(lambda (value-form)
  						    `(setq ,lisp-name ,value-form))
  			     :side-effects (make-instance 'side-effects :used-variables (list variable)
  							  :variables-used-before-assigned (list variable))
  			     :type func-type
  			     :argument-types '()
  			     :result-types (list type)
  