anchor.diff:  
   (define-parser arithmetic-up-13-parser
     (consecutive (lambda (var type-spec by form1)
  -		 (declare (ignore from to by))
  +		 (declare (ignore from by))
   		 (let ((by-var (gensym)))
   		   (make-instance 'for-as-arithmetic
   		     :bindings `((,var ,0)
  
positive.code: 
  (define-parser arithmetic-up-13-parser
    (consecutive (lambda (var type-spec to form1)
  		 (declare (ignore from to by))
  		 (let ((to-var (gensym)))
  		   (make-instance 'for-as-arithmetic
  		     :bindings `((,var ,0)
  				 (,to-var,form1))
  		     :termination `(when (> ,var ,to-var) (go end))
  		     :step `(incf ,var))))
  	       (singleton #'identity
  			  (lambda (x) (and (symbolp x) (not (constantp x)))))
  	       'type-spec-parser
  	       (alternative (keyword-parser 'to)
  			    (keyword-parser 'upto))
  	       (singleton #'identity (constantly t))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  
negative.code: 			  (lambda (x) (and (symbolp x) (not (constantp x)))))
  	       'type-spec-parser
  	       (alternative (keyword-parser 'to)
  			    (keyword-parser 'upto)
  			    (keyword-parser 'below))
  	       (singleton #'identity (constantly t))
  	       (keyword-parser 'by)
  	       (singleton #'identity (constantly t))))
  