# File app/models/proposal.rb, line 42
  def dont_change_conference
    prev_state = self.class.find_by_id(self.id)
    return true if self.conference_id == prev_state.conference_id
    self.errors.add(:conference_id,
                    _('An already submitted proposal can not be moved ' +
                      'to a different conference'))
    false
  end