anchor.diff:  
   (in-package "SPATIAL-TREES-IMPL")
   
  -(defparameter *kinds* '(:r :greene :r*))
  +(defparameter *kinds* '(:r :greene :r* :x))
   
   (defun make-random-rectangle (&optional (x-bias 0.0) (y-bias 0.0))
     (let* ((lx (+ (random 1.0) x-bias))
  
positive.code:                      for r = (make-random-rectangle)
                       collect (cons (lows r) (highs r))))
           (rectfun (lambda (x) (make-rectangle :lows (car x) :highs (cdr x))))
           (tree (make-spatial-tree :r :rectfun rectfun)))
      (dolist (r list)
        (insert r tree))
      (let* ((r (make-random-rectangle))
  
negative.code:          (list (loop repeat n collect (make-random-rectangle)
                       collect (make-random-rectangle -2.0 -2.0)
                       collect (make-random-rectangle 2.0 2.0)))
           (tree (make-spatial-tree kind :rectfun #'identity)))
      (dolist (r list)
        (insert r tree))
      (let ((r (make-rectangle :lows '(0.0 0.0) :highs '(1.0 1.0))))
  