  The polarization transfer coefficient $K_y^{y'}$ for the $^2$H$(\vec{d},
\vec{p})^3$H reaction at energies $E_{\rm lab.} = 30$, 50, 70, and 90keV is
calculated using the four-body Faddeev-Yakubovsky equation. We employ a
separable type of the Paris potential. The experimental data [Phys. Rev. {\bf
C64}, 047601 (2001)] agrees with our solution at the scattering angle
$\theta_{\rm c.m.}=0^\circ$, and there is no discrepancy pointed out in that
paper. We found that the $K_y^{y'}$ is sensitive to the incident deuteron
energy at this angle.
