code: def back(self, *fields):
          '''Return the back pair of the structure'''
          ts = self.irange(-1, -1, fields=fields)
          if ts:
              return ts.end(), ts[0f back(self, *fields):
          '''Return the back pair of the structure'''
          ts = self.irange(-1, -1, fields=fields)
          if ts:
              return ts.end(), ts[0]
docs: Return the back pair of the structure