Consistently use n for spatial dimension, not d.
Various minor text fixes, and some equation layout improvements.
Update index notation:
- a,b,c for particle labels
- i,j,k for spatial indices
- \alpha,\beta for spatial multi-indices
Be more consistent with momentum map order notation.
Indicate suppressing notation in K = K_{k,\sigma}.
Add two todo notes.
Use more standard (?) notation for dual of tangent map.
Henry please revert if you disagree.