  The solutions to the zero-sound frequency equation and pion dispersion
equation are considered for the different values of the parameters of the
effective particle-hole interaction. The branches of solutions, responsible for
the long-wave instability [Pomeranchuk] of the nuclear matter \omega_P(k) are
presented for the both equations. It is shown that in the pion dispersion
equation the solutions \omega_P(k) result in the instability not only for
values of the spin-isospin constant g'\leq -1/2, violating stability criteria,
but for all g' < g'_p (|g'_p|\ll 1 and g'_p < 0). At g' > g'_p the branches
\omega_P(k) turn into the solutions responsible for pion condensation.
