anchor.diff:  
   (defun setup-for-next-line (xp Qentry)
     (let* ((out-point (BP<-TP xp (Qpos xp Qentry)))
  -	 (prefix-end
  -	   (cond ((member (Qkind xp Qentry) '(:unconditional :fresh))
  -		  (non-blank-prefix-ptr xp))
  -		 (T (prefix-ptr xp))))
  -	 (change (- prefix-end out-point)))
  +         (prefix-end
  +           (cond ((member (Qkind xp Qentry) '(:unconditional :fresh))
  +                  (non-blank-prefix-ptr xp))
  +                 (T (prefix-ptr xp))))
  +         (change (- prefix-end out-point)))
       (setf (charpos xp) 0)
       (when (plusp change)                  ;almost never happens
         (check-size xp buffer (+ (buffer-ptr xp) change)))
       (replace (buffer xp) (buffer xp) :start1 prefix-end
  -	     :start2 out-point :end2 (buffer-ptr xp))
  +             :start2 out-point :end2 (buffer-ptr xp))
       (replace (buffer xp) (prefix xp) :end2 prefix-end)
       (incf (buffer-ptr xp) change)
       (decf (buffer-offset xp) change)
  
positive.code: ;same code in both cases.
  
  (defvar *bq-list* #+:lucid 'lucid-runtime-support:bq-list
  	          #+:symbolics 'si:xr-bq-list)
  (defvar *bq-list** #+:lucid 'lucid-runtime-support:bq-list*
  	           #+:symbolics 'si:xr-bq-list*)
  (defvar *bq-cons* #+:lucid 'lucid-runtime-support:bq-cons
  	          #+:symbolics 'si:xr-bq-cons)
  (defvar *bq-append* #+:lucid 'lucid-runtime-support:bq-append
  	            #+:symbolics 'si:xr-bq-append)
  (defvar *bq-nconc* #+:lucid 'lucid-runtime-support:bq-nconc
  	           #+:symbolics 'si:xr-bq-nconc)
  
  (defun bq-print (xp obj)
    (funcall (formatter "`~W") xp (bqtify obj)))
  
  (defvar *bq-vector* #+:lucid 'lucid-runtime-support:bq-nconc
  	           #+:symbolics (list nil)) ;turned off
  (defvar *bq-list-to-vector* #+:lucid 'lucid-runtime-support:bq-nconc
  	                    #+:symbolics (list nil)) ;turned off
  
  (defun bq-vector-print (xp obj)
    (funcall (formatter "`#~W") xp (car (bqtify obj))))
  
negative.code:   (let ((old-prefix 0) (old-suffix 0) (old-non-blank 0))
      (when (not (minusp (prefix-stack-ptr xp)))
        (setq old-prefix (prefix-ptr xp)
              old-suffix (suffix-ptr xp)
              old-non-blank (non-blank-prefix-ptr xp)))
      (incf (prefix-stack-ptr xp) +prefix-stack-entry-size+)
      (check-size xp prefix-stack (prefix-stack-ptr xp))
      (setf (prefix-ptr xp) old-prefix)
  