def reference_string(self):
        """ Get the authors part of the usual citation of scientific literature i.e.:

            Lastname F et al., YYYY if there are more than 2 authors
            Lastname1 F1 and Lastname2 F2, YYYY if there are 2 authors
            Lastname F, YYYY if there is only one author

            Input tuple with (lastname, firstname, initials)
        """
        # If there are more than 2 authors return a string
        if len(self.authors) > 2:
            return "{0} et al., {1}".format(self.authors[0].display_str, self.year)
        elif len(self.authors) == 2:
            return "{0} and {1}, {2}".format(self.authors[0].display_str,
                                             self.authors[1].display_str,
                                             self.year)
        elif self.authors:
            return "{0}, {1}".format(self.authors[0].display_str, self.year)
        else:
            return ""