- All bond-lengths which are within 0.0001Å are set equal.
- All bond-angles which are within 0.0057 are set equal.
- All dihedral angles which are within 0.0057 are set equal.
- All dihedral angles which are within 0.0057 of the negative of an existing dihedral are set equal to the negative of the existing dihedral.

These 'rules' are a re-wording of internal `SYMMETRY` functions 1, 2, 3,
and 14. The `.arc` file will include the symmetry data. In order to
change the `.arc` file symmetry data into normal symmetry data, change
`AUTOSYM` in the `.arc` file to `SYMMETRY`.

AUTOSYM only adds symmetry to coordinates that can be optimized. If a
coordinate has an optimization flag of "0", it will not be looked at by AUTOSYM.

Consider benzene: If someone built the Z-matrix in internal coordinates, they
would likely mark the C-C and C-H distances as optimizable, and lock the angles
and dihedrals. If they used AUTOSYM, then it would symmetry-relate all the C-C
distances and all of the C-H distances, but leave the angles and dihedrals
untouched.