anchor.diff:  (define-parser arithmetic-up-7-parser
     (consecutive (lambda (var type-spec from form1 to form2)
   		 (declare (ignore from to))
  -		 (let ((to-var (gensym))
  -		       (by-var (gensym)))
  +		 (let ((to-var (gensym)))
   		   (make-instance 'for-as-arithmetic
   		     :bindings `((,var ,form1)
   				 (,to-var ,form2))
  
positive.code: 		   (make-instance 'for-as-arithmetic
  		     :bindings `((,to-var ,form1)
  				 (,by-var ,form2)
  				 (,from-var ,form3))
  		     :termination `(when (>= ,var ,to-var) (go end))
  		     :step `(incf ,var ,by-var))))
  	       (singleton #'identity
  
negative.code: 		       (by-var (gensym)))
  		   (make-instance 'for-as-arithmetic
  		     :bindings `((,by-var ,form1)
  				 (,to-var ,form2)
  				 (,var ,form3))
  		     :termination `(when (>= ,var ,to-var) (go end))
  		     :step `(incf ,var ,by-var))))
  	       (singleton #'identity
  