- symbols can have a LaTeX name, e.g. symbol s("s", "\\sigma");

- symbols can have a LaTeX name, e.g. symbol s("s", "\\sigma");
- LaTeX output of indexed objects and tensors is much nicer
- simplify_indexed() can do arbitrary contractions in Dirac gamma strings
- constructing expressions like
    (x * dirac_ONE() + dirac_ONE()) * dirac_gamma(mu)
  resulted in an exception because mul::simplify_ncmul() wasn't implemented
  (maybe afrink didn't anticipate that an implementation would really be
  needed...)