Returns the given course and all other courses it is
        crosslisted with.

def find_course_and_crosslistings(self, partial):
        """Returns the given course and all other courses it is
        crosslisted with.
        """
        course = self.find_course(partial)
        crosslisted = self.crosslisted_with(course.crn)
        return (course,) + tuple(map(self.find_course_by_crn, crosslisted))