Third, the sometimes bad reputation of the Kohn-Sham noninteracting system stems from the fact that it is often used in place of the real system -not to yield simply its density, but also any other observable, in particular, spectral functions. Of course, this can lead to strong disagreement with the truth -and the band gap is just one example. Maybe we should just be more precise in saying what we are doing here -namely, that we use the Kohn-Sham expression (which is a functional of the density) for a given observable as an approximate functional because we do not know a better one? This doesn't change the results, but it sounds a little more fair to the Kohn-Sham noninteracting system.