anchor.diff:    (multiple-value-bind (x y) (point-position point)
       (region-contains-position-p xs x y)))
   
  -;;; ---- interval sums ----------------------------------------------------------------------------------
  +;;; ---- interval sums ---------------------------------------------------------
   
   (defun isum-union* (xs ys)        (isum-op xs ys boole-ior   0 0 nil))
   (defun isum-difference* (xs ys)   (isum-op xs ys boole-andc2 0 0 nil))
  
positive.code: (defclass standard-polygon (polygon)
    ((points :initarg :points)) )
  
  ;;; ---- 2.5.3.1 Constructors for CLIM Polygons and Polylines  ---------------------------
  
  (defun coord-seq->point-seq (sequence)
    (let ((res nil))
  
negative.code:   (or (eq a b)
        (region-equal +nowhere+ (region-difference b a))))
    
  ;;;; ===========================================================================
  
  (defmethod bounding-rectangle* ((a standard-line))
    (with-slots (x1 y1 x2 y2) a
  