anchor.diff:                     val (rec-lsts (mapcar #'cdr lsts))))))
              (rec-seqs (seqs)
                (if (not (find 0 seqs :key #'length))
  -               (let ((val (apply gen-fn (mapcar (p #'elt _ 0) seqs))))
  +               (let ((val (apply gen-fn (mapcar (p (elt _ 0)) seqs))))
                    (if (funcall check-key val)
                      val (rec-seqs (mapcar #'drop seqs)))))))
       (if (eql (type-of seq) 'cons)
  
positive.code:   (let ((head-pos (position-if-list pred seq :key key)))
      (values
        (mapcar
          (p #'subseq seq)
          (if mark-discard? (mapcar #'1+ head-pos) head-pos)
          (drop (append1 head-pos (length seq))))
        (subseq seq 0 (car head-pos)))))
  
negative.code:   (let ((tail-pos (position-if-list pred seq :key key)))
      (values
        (mapcar
          (p (subseq seq))
          (cons 0 (mapcar #'1+ tail-pos))
          (if mark-discard?  tail-pos (mapcar #'1+ tail-pos)))
        (if tail-pos (subseq seq (1+ (last1 tail-pos))) seq))))
  