equation icon  [ a a2 a b 3] gtt = - 1 + 2aa ^y + (aay^ ) + Eab^y ^y + O(s ) , (135) 2- b c d 3 gta = - 3 eabcB d^y ^y + O(s ), (136) ( c d) 3 gab = dab 1 - Ecd^y ^y + O(s ). (137)