field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,related_name='periodfrom',to='chronos.TimePeriod',verbose_name='Effective start period of event'),
),
migrations.AddField(
model_name='event',
name='periodto',
field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,related_name='periodto',to='chronos.TimePeriod',verbose_name='Effective end period of event'),