def method_missing(symbol, *args)
      (args.empty? and labeled.has_key?(symbol)) ? labeled[symbol] : super
    end
def method_missing(symbol, *args)
      (args.empty? and labeled.has_key?(symbol)) ? labeled[symbol] : super
    end
Return +true+ if the node has the same value as +other+, i.e. +other+
 is an instance of the same class and has equal children and attributes
 and the children are labeled the same.

 @return [Boolean] +true+ the node has the same value as +other+
 Allow labeled children to be accessed as methods.