  In our previous work (E. Kogan, Phys. Rev. B 84, 115119 (2011)) we presented
calculation of RKKY interaction between two magnetic impurities in graphene
based on Matsubara Green's functions (MGF) in the coordinate -- imaginary time
representation. Now we present the calculation based on MGF in the coordinate
-- frequency representation. We claim that both approaches have an important
advantage over those based on zero temperature Green's functions (ZTGF), which
are very briefly reviewed in the beginning of the present work. The MGF
approaches, in distinction to the ZTGF approaches, operate only with the
convergent integrals from the start to the end of the calculation. The
coordinate -- frequency representation for the MGF turns out to be as
convenient as the coordinate -- imaginary time representation and allows to
easily consider the cases of doped and gapped graphene.
