  Cauchy initial value problem on a hyperboloid is proved to define a
Hamiltonian system, provided the radiation data at null infinity are also taken
into account, as a part of Cauchy data. The "Trautman-Bondi mass", supplemented
by the "already radiated energy" assigned to radiation data, plays role of the
Hamiltonian function. This approach leads to correct description of the corner
conditions.
