Equation Icon  ∫ ( ) Dab ≡ √-1---δ-- dnx √ −-g RcdefRcdef − RcdRcd − gδgab gab( ) = --- RcdefRcdef− RcdRcd + □R − 2RacdeRbcde− 2RacbdRcd + 4RacRcb − 3□Rab + ∇a ∇bR. 2 (37 )