anchor.diff:                (make-s-diet-node :bottom max-int-bottom :top top :left l-subtree-w/o-max-interval :right right)
                 (make-s-diet-node :bottom bottom :top top :left left :right right))))))
   
  -(defun join-right (a-diet-node)
  +
  +(defun join-right-2 (a-diet-node)
     (with-slots (top bottom left right) a-diet-node
       (if (null right)
           a-diet-node
  
positive.code:                              :right (s-diet-node-right a-diet-node)
                               :left tree-w/o-min-interval))))))
  
  (defun join-left (a-diet-node)
    (with-slots (top bottom left right) a-diet-node
      (if (null left)
          a-diet-node
  
negative.code: (defstruct s-diet-node bottom top left right)
  
  ;; Go right until you hit a node without a right offspring.
  ;; When this happens, return node values and a tree that leads
  ;; to this node, w/o this very node.
  ;; Returns the following values:
  ;; - bottom boundary of a rightmost leaf
  ;; - top boundary of a rightmost leaf
  