code: def left_and_rights_valid?
        all.detect { |node|
          node.send(left_field_name).nil? ||
            node.send(right_field_name).nil? ||
            node.send(left_field_name) >= node.send(right_field_name) ||
            !node.parent.nil? && (
              node.send(left_field_name) <= node.parent.send(left_field_name) ||
              node.send(right_field_name) >= node.parent.send(right_field_name)
          )
        }.nil?
      end
docs: Warning: Very expensive!  Do not use unless you know what you are doing.