Abstract:
It is shown that a classical Hamiltonian wave system that possesses at
least one additional integral of the motion with quadratic principal
part has an infinite number of such integrals in the cases of both
nondegenerate and degenerate dispersion laws. Conditions under which
in a space of dimension $d\geqslant 2$ a system with nondegenerate dispersion
law is completely integrable and its Hamiltonian can be reduced to
normal form are found. In the case of a degenerate dispersion law
integrals are not sufficient for complete integrability.