anchor.diff:    (when (current-owner history)
       (all-children (current-owner-node history))))
   
  -(export-always 'all-owned-children)
  -(defmethod all-owned-children ((owner owner))
  +(export-always 'all-contiguous-owned-children)
  +(defmethod all-contiguous-owned-children ((owner owner))
     "Return a list of all the children owned by OWNER, recursively."
     (map-tree #'identity (current owner) :flatten t
                                          :children-function #'owned-children))
   
  -(defmethod all-owned-children ((history history))
  +(defmethod all-contiguous-owned-children ((history history))
     "Return a list of all the children owned by HISTORY's current owner,
   recursively."
     (when (current-owner history)
  -    (all-owned-children (current-owner history))))
  +    (all-contiguous-owned-children (current-owner history))))
   
   (export-always 'all-parents)
   (defmethod all-parents ((node node))
  
positive.code:     (when root
        (cons root (all-children root)))))
  
  (export 'all-owned-nodes)
  (defmethod all-owned-nodes ((owner owner))
    "Return a list of all owner nodes, in depth-first order."
    (let ((owner-root (first (all-owned-parents owner))))
      (when owner-root
        (cons owner-root (all-owned-children owner-root)))))
  
  
  
  
negative.code:   (when (current-owner history)
      (all-parents (current-owner-node history))))
  
  (export-always 'all-contiguous-owned-parents)
  (defmethod all-contiguous-owned-parents ((owner owner))
    "Return a list of parents of owned by OWNER, starting from its current node,
  recursively.
  First parent comes first in the resulting list."
    (when (and (parent owner)
               (owned-p owned (parent owner)))
      (cons (parent owner)
            (all-contiguous-owned-parents (current owner)))))
  
  (defmethod all-contiguous-owned-parents ((history history))
    "Return a list of parents of owned by HISTORY current owner, starting from its
  current node, recursively.  First parent comes first in the resulting list."
    (when (current-owner history)
      (all-contiguous-owned-parents (current-owner history))))
  
  (export-always 'all-forward-children)
  (defmethod all-forward-children ((owner owner))
  