9VARIABLES: level - CYANA variable

Initial value: 0

This variable specifies the "minimization level", i.e. the maximal
difference between the residue indices of the two atoms in a distance
restraint that is considered when calculating the target function. If
level = 0, then only intraresidual restraints will be considered,
if level = 1, then intraresidual and sequential distance restraints
will be considered.

The use of minimization levels is the central idea of the variable
target function method.

Further reading:

- Braun & Go, J. Mol. Biol. 186, 611-626 (1985).
- Guentert et al. J. Mol. Biol. 217, 517-530 (1991).
