Equation Icon  f abcd = − ⊥𝜀ab(δcAd − δdAc ) + 12𝒮R (Πacqbd − Πadqbc), (4.1 ) a a a a a a F bcd = f bcd − δc (Q db − Qbd ) + δd(Q cb − Qbc ) + +QaceQbde + QecaQedb − QadeQbce − QedaQecb, (4.2 )