def unlink_node(child_node)
      if @smaller == child_node
        @smaller = nil
      elsif @equal == child_node
        @equal = nil
      elsif @larger == child_node
        @larger = nil
      else
        PEROBS.log.fatal "Cannot unlink unknown child node with address " +
          "#{child_node.node_address} from #{to_s}"
      end
      @tree.cache.insert(self)
    end
def unlink_node(child_node)
      if @smaller == child_node
        @smaller = nil
      elsif @equal == child_node
        @equal = nil
      elsif @larger == child_node
        @larger = nil
      else
        PEROBS.log.fatal "Cannot unlink unknown child node with address " +
          "#{child_node.node_address} from #{to_s}"
      end
      @tree.cache.insert(self)
    end
Remove a smaller/equal/larger link from the current node.
 @param child_node [SpaceTreeNodeLink] node to remove