docs: def JMS_to_Fierz_chrom(C, qq):
      """From JMS to chromomagnetic Fierz basis for Class V.
      qq should be of the form 'sb', 'ds' etc."""
      if qq[0] in dflav:
          s = dflav[qq[0]]
          b = dflav[qq[1]]
          return {
                  'F7gamma' + qq : C['dgamma'][s, b],
                  'F8g' + qq : C['dG'][s, b],
                  'F7pgamma' + qq : C['dgamma'][b, s].conj(),
                  'F8pg' + qq : C['dG'][b, s].conj()
                      }
      else:
          u = uflav[qq[0]]
          c = uflav[qq[1]]
          return {
                  'F7gamma' + qq : C['ugamma'][u, c],
                  'F8g' + qq : C['uG'][u, c],
                  'F7pgamma' + qq : C['ugamma'][c, u].conj(),
                  'F8pg' + qq : C['uG'][c, u].conj()
                      }