def saturdays_of_weekends(self) -> Set[datetime.date]:
        """
        Returns the dates of all Saturdays that are part of weekends that this
        interval covers (each Saturday representing a unique identifier for
        that weekend). The Saturday itself isn't necessarily the part of the
        weekend that the interval covers!
        """
        startdate = self.start.date()
        enddate = self.end.date()
        ndays = (enddate - startdate).days + 1
        saturdays = set()
        for i in range(ndays):
            date = startdate + datetime.timedelta(days=i)
            if is_saturday(date):
                saturdays.add(date)
            elif is_sunday(date):
                saturdays.add(date - datetime.timedelta(days=1))
        return saturdays