anchor.diff:            gcp gcs
             length< length<= length> length>=
             longer longest
  -          cut
             ordering
             bestn
             extrema
  
positive.code:              (x y)
               (y x))))
      (reduce #'shorter seqs)))
  
  (defun cut (seq indices)
    "Divide up SEQ at INDICES.
  
       (cut (iota 8) '(2 4 6))
       => ((0 1) (2 3) (4 5) (6 7))
  
  From Q."
    (unless (eql 0 (first indices))
      (push 0 indices))
    (etypecase seq
      (list
       (let ((offsets (mapcar #'- (rest indices) indices)))
         (collecting*
           (nlet cut ((list seq)
                      (offsets offsets))
             (let ((offset (first offsets)))
               (if (no offset)
                   (collect list)
                   (let ((tail (nthcdr offset list)))
                     (collect (ldiff list tail))
                     (cut tail (rest offsets)))))))))
      (sequence
       (loop for (start . rest) on indices
             for end = (car rest)
             collect (subseq seq start end)))))
  
  (defun slice-bounds (seq start end)
    "Normalize START and END, which may be negative, to offsets
  
negative.code: (assert (equal (partitions (list #'oddp #'evenp) '(0 1 2 3 4 5 6 7 8 9))
                 '((1 3 5 7 9) (0 2 4 6 8))))
  
  (defun list-assort (list &key (key #'identity) (test #'eql) (start 0) end)
    (declare (list list) (optimize speed))
    (fbind ((key key) (test test))
  