xAct-contrib/xPand — pull request #6 by CyrilPitrou (2013-11-13 11:00:07+00:00)
Title: Normal vector with by products (extrinsic curvature, accceleration) at a working stage. Comments and examples provided.

The perturbation of curvature tensors associated with the metric on the (perturbed) constant time hypersurfaces, is not implemented yet. This would require to use the Gauss-Codazzi relations, but at the perturbed level. This is left for future work.