anchor.diff:       finally (return t)))
   
   (defun check-dotree (tree bitvector)
  +  (declare (type simple-bit-vector bitvector))
     (let ((new (bit-xor bitvector bitvector)))
       (trees:dotree (x tree)
         (setf (aref new x) 1))
  
positive.code:     t))
  
  (defun check-reduce (tree bitvector)
    (loop with tree-sum = (trees:reduce tree #'+)
       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
  