equation icon  1- S[pq][ik] := 4 (Fpqik - Fqpik + Fikpq- Fkipq), 1 Fpqik = Rpqik + -(gpqfki + gpkfq;i + gqifp;k- gpifq;k- gqkfp;i) 2 + 1-(f g f + f g f + g g f fr), 2 qp;[k i] p q;[k i] p[i k]q r