anchor.diff:  		   (make-instance 'for-as-arithmetic
   		     :bindings `((,to-var ,form1)
   				 (,by-var ,form2)
  -				 (,from-var ,form3))
  +				 (,var ,form3))
   		     :termination `(when (>= ,var ,to-var) (go end))
   		     :step `(incf ,var ,by-var))))
   	       (singleton #'identity
  
positive.code: (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)))
  		   (make-instance 'for-as-arithmetic
  		     :bindings `((,var ,form1)
  				 (,to-var ,form2))
  
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
  