Singularity of Green dyadic for bi-isotropic media

The singularity of the Green dyadic for the general bi-isotropic medium is constructed through decomposition of the bi-isotropic problem in two simple isotropic problems. It is seen that, in contrast to the isotropic medium case, the singularity cannot be written in terms of a simple delta function term but it involves a second term containing the derivative of the delta function as well