8FUNCTIONS: iprev - CYANA function

Synopsis: iprev(<integer>) = <integer>

For the rotatable dihedral angle with the given index, between 1 and
ndfree, this function returns the index of the rotatable dihedral
angle that precedes it in the tree structure of dihedral angles. For
the first rotatable dihedral angle, the function returns iprev(1) = 0.

Optionally, the <integer> dihedral angle index can be replaced by a
string consisting of the dihedral angle name and the residue number,
separated by a blank or a period, '.'.
