Examples:

It is assumed that there are currently three data sets:

XSPEC> arf a,b,c       ! New files for the auxiliary response 
                            are given for all three files.

XSPEC> arf 2 none      ! No auxiliary response will be used for 
                            the second file.

XSPEC> arf,,d.fits     ! d.fits becomes the auxiliary response 
                            for the second file.