def obo(self):
        """str: the `Relationship` serialized in an ``[Typedef]`` stanza.

        Note:
            The following guide was used:
            ftp://ftp.geneontology.org/pub/go/www/GO.format.obo-1_4.shtml
        """

        lines = [
            "[Typedef]",
            "id: {}".format(self.obo_name),
            "name: {}".format(self.obo_name)
        ]
        if self.complementary is not None:
            lines.append("inverse_of: {}".format(self.complementary))
        if self.symmetry is not None:
            lines.append("is_symmetric: {}".format(self.symmetry).lower())
        if self.transitivity is not None:
            lines.append("is_transitive: {}".format(self.transitivity).lower())
        if self.reflexivity is not None:
            lines.append("is_reflexive: {}".format(self.reflexivity).lower())
        if self.comment:
            lines.append("comment: {}".format(self.comment))
        return "\n".join(lines)
str: the `Relationship` serialized in an ``[Typedef]`` stanza.

        Note:
            The following guide was used:
            ftp://ftp.geneontology.org/pub/go/www/GO.format.obo-1_4.shtml