def domain_name(self, levels=1):
        """
        Produce an Internet domain name with the specified number of
        subdomain levels.

        >>> domain_name()
        nichols-phillips.com
        >>> domain_name(2)
        williamson-hopkins.jackson.com
        """
        if levels < 1:
            raise ValueError("levels must be greater than or equal to 1")
        if levels == 1:
            return self.domain_word() + '.' + self.tld()
        else:
            return self.domain_word() + '.' + self.domain_name(levels - 1)
Produce an Internet domain name with the specified number of
        subdomain levels.

        >>> domain_name()
        nichols-phillips.com
        >>> domain_name(2)
        williamson-hopkins.jackson.com