For universal spacetimes, all rank-2 tensors constructed from the metric,
Riemann tensors, and its covariant derivatives of arbitrary order are
proportional to the metric. Consequently, all vacuum field equations of
generalized theories of gravity following from Lagrangian constructed from
the Riemann tensors and its covariant derivatives of arbitrary order are... more
Riemann tensors, and its covariant derivatives of arbitrary order are
proportional to the metric. Consequently, all vacuum field equations of
generalized theories of gravity following from Lagrangian constructed from
the Riemann tensors and its covariant derivatives of arbitrary order are... more