  We suggest that the phonon dispersion in cuprates becomes strongly
anisotropic due to interaction with spin waves; moreover the phonon dispersion
becomes singular along $|k_x|=|k_y|$ directions. This would allow more
electrons to form Cooper pairs and increase temperature of the superconducting
transition. The interaction of phonons with spin waves is more important than
the interaction of phonons with free electrons, because spin waves do not have
the Fermi surface constrain.
