Equation Icon  f abcd = - _L eab(dcAd - ddAc) + 1SR (TTacqbd- TTadqbc) , (20) a a a a 2 a a F bcd = f bcd- dc (Q db- Qbd ) + dd(Q cb - Qbc ) + +QaceQbde + QecaQedb - QadeQbce - QedaQecb, (21)