anchor.diff:    (let ((head-pos (position-if-list pred seq :key key)))
       (values
         (mapcar
  -        (p #'subseq seq)
  +        (p (subseq seq))
           (if mark-discard? (mapcar #'1+ head-pos) head-pos)
           (drop (append1 head-pos (length seq))))
         (subseq seq 0 (car head-pos)))))
  
positive.code: (defmacro >case (expr &body clauses)
    (with-gensyms (v)
      `(let ((,v ,expr))
         (cond ,@(mapcar (p #'>case-cl-expand v) clauses)))))
  
  ;;; July 30th 2012, chiku
  ;;; It's ported from LL(k) project.
  
negative.code: ;;; Current version explains the algorithm pretty well, even though
  ;;; it might perform bad.
  (defun group-filter (n fn lst)
    (filter (p (apply fn)) (group lst n)))
  
  ;;; Sep 30th 2011, chiku
  ;;; LISTFORK-IF function
  