By definition, Rσμνρ=−Rσμνρ Rρσμν=−Rσρμν Rρσμν=Rμνρσ Rρ[σμν]=Rρσμν+Rρμνσ+Rρνσμ=0 Bianchi Identity ∇[λRρσ]μν=0 Ricci Tensor Rμν=Rμλνλ=Rνμ Ricci Scalar R=gμνRμν ContractedBianchi Identity ∇μRρμ=21∇ρR DefiningEinstein-Tensor Gμν=Rμν−21gμνR ∇μGμν=0