  The interaction energy of the neutrons due to massless neutrino exchange in a
neutron star has recently been proved, using an effective theory, to be
extremely small and infrared-safe. Our comment here is of conceptual order: two
approaches to compute the total interaction energy density have recently been
proposed. Here, we study the connection between these two approaches. From CP
invariance, we argue that the resulting interaction energy has to be even in
the parameter $b=-G_F n_n /\sqrt{2}$, which expresses the static neutrino
potential created by a neutron medium of density $n_n$.
