  The equation of motion method (EOM) is one of the approximations to calculate
transport coefficients of interacting electron systems. The method is known to
be useful to examine high-temperature properties. However, sometimes a naive
application of the EOM fails to capture an important physics at low-energy
scale, and it happens in recent preprints cond-mat/0309458 and cond-mat/0308413
which study a series of quantum dots. These preprints concluded that a
unitarity-limit transport due to the Kondo resonance, which has been deduced
from a Fermi-liquid behavior of the self-energy at T=0, $\omega=0$ [A.O., PRB
{\bf 63}, 115305 (2001)], does not occur. We show that the EOM self-energy
obtained with a finite cluster has accidentally a singular $1/\omega$
dependence around the Fermi energy, and it misleads one to the result
incompatible with a Fermi-liquid ground state.
