text: Fig 5 shows the optical sum in NS and SCS in clean 
  and dirty limits (the parameters are stated in the ﬁg- 
  ure). This plot shows that the Kubo sums are almost 
  completely recovered by integrating up to the bandwidth 
  of 1eV : the recovery is 95% in the clean limit and ∼ 90% 
  in the dirty limit. In Fig 6 we plot ∆W (ωc) as a function 
  of ωc in clean and dirty limits. ∆W (∞) is now non-zero, 
  in agreement with Fig. 4 and we also see that there is  For completeness, we ﬁrst present some well known 
  results about the conductivity and optical integral for a 