docs: def _Bern_to_JMS_I(C, qq):
      """From Bern to JMS basis for $\Delta F=2$ operators.
      `qq` should be 'sb', 'db', 'ds' or 'cu'"""
      if qq in ['sb', 'db', 'ds']:
          dd = 'dd'
          ij = '{}{}'.format(dflav[qq[0]] + 1, dflav[qq[1]] + 1)
      elif qq == 'cu':
          dd = 'uu'
          ij = '{}{}'.format(uflav[qq[0]] + 1, uflav[qq[1]] + 1)
      else:
          raise ValueError("not in Bern_I: ".format(qq))
      ji = ij[1] + ij[0]
      d = {"V{}LL_{}{}".format(dd, ij, ij): C['1' + 2 * qq],
           "S1{}RR_{}{}".format(dd, ji, ji): C['2' + 2 * qq].conjugate() + C['3' + 2 * qq].conjugate() / 3,
           "S8{}RR_{}{}".format(dd, ji, ji): 2 * C['3' + 2 * qq].conjugate(),
           "V1{}LR_{}{}".format(dd, ij, ij): -C['4' + 2 * qq] / 6 - C['5' + 2 * qq] / 2,
           "V8{}LR_{}{}".format(dd, ij, ij): -C['4' + 2 * qq],
           "V{}RR_{}{}".format(dd, ij, ij): C['1p' + 2 * qq],
           "S1{}RR_{}{}".format(dd, ij, ij): C['2p' + 2 * qq] + C['3p' + 2 * qq] / 3,
           "S8{}RR_{}{}".format(dd, ij, ij): 2 * C['3p' + 2 * qq],
           }
      if qq == 'cu':
          # here we need to convert some operators that are not in the basis
          for VXY in ['VuuRR', 'V1uuLR', 'V8uuLR', 'VuuLL']:
              d[VXY + '_1212'] = d.pop(VXY + '_2121').conjugate()
      return d