docs: def Fierz_to_Bern_chrom(C, dd, parameters):
      """From Fierz to chromomagnetic Bern basis for Class V.
      dd should be of the form 'sb', 'ds' etc."""
      e = sqrt(4 * pi * parameters['alpha_e'])
      gs = sqrt(4 * pi * parameters['alpha_s'])
      if dd == 'sb' or dd == 'db':
          mq = parameters['m_b']
      elif dd == 'ds':
          mq = parameters['m_s']
      else:
          KeyError("Not sure what to do with quark mass for flavour {}".format(dd))
      return {
          '7gamma' + dd : gs**2 / e / mq * C['F7gamma' + dd ],
          '8g' + dd : gs / mq * C['F8g' + dd ],
          '7pgamma' + dd : gs**2 / e /mq * C['F7pgamma' + dd],
          '8pg' + dd : gs / mq * C['F8pg' + dd]
              }