Chapter 19
Exer. 19.14 Discrete analogue of the stress-energy tensor?
Exer. 19.16 Ricci tensor has info about volume acceleration: a nice illustration of Lie derivatives
Exer. 19.16 Comment on above solution
Exer. 19.16 yet another solution
Exer. 19.18 trace-reversed Ricci tensor has 0 divergence
Exer. 19.21 Ricci tensor is 0 if trace-reversed Ricci tensor is 0