anchor.diff:       finally (return t)))
   
   (defun check-selection (tree bitvector)
  +  (declare (type simple-bit-vector bitvector))
     (unless (zerop (trees:size tree))
       (loop for start = 0 then (1+ x)
          for x = (position 1 bitvector :start start)
  
positive.code:     (funcall test tree bitvector)))
  
  (defun check-equivalency (tree bitvector)
    (loop
       for start = 0 then (1+ x)
       for x = (position 1 bitvector :start start)
  
negative.code:      finally (return t)))
  
  (defun check-forward-position-nil (tree bitvector)
    (declare (type simple-bit-vector bitvector))
    (loop for start = 0 then (1+ x)
       for x = (position 0 bitvector :start start)
       while x
  