From: ellocomateo@free.fr   
      
   It turns out my question is related to this paper:   
   http://prola.aps.org/abstract/PR/v130/i3/p919_1   
      
   In particular, in Eq. 4.4a, what is the meaning of \partial_k E_l(w1)?   
   Does the k index need be the same as the l one, for \partial_k E_l(w1)   
   to be non zero?   
      
   Concerning Eq 4.13, what is the meaning of \nabla\cdot applied on the   
   electric quadrupole Q_{ki}(2w) of Eq 4.4a?   
      
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