Translate a project node into latex qtree node.
        :param node: a treebrd node
        :return: a qtree subtree rooted at the node

def project(self, node):
        """
        Translate a project node into latex qtree node.
        :param node: a treebrd node
        :return: a qtree subtree rooted at the node
        """
        child = self.translate(node.child)
        return '[.${op}_{{{attributes}}}$ {child} ]'\
            .format(op=latex_operator[node.operator],
                    attributes=', '.join(node.attributes.names),
                    child=child)