8FUNCTIONS: idcoa - CYANA function

Synopsis: idcoa(<integer>,<integer>) = <integer>

This function returns the index of the first (if the first argument
is 1) or second (if the first argument is 2) atom that is involved
in the distance restraint whose index is given as the second argument.

The upper and lower limit distance restraints are indexed from 1 to
ndco in the order in which they were read from the input file(s).
