  The s-channel unitarity condition for the imaginary part of the hadronic
elastic scattering amplitude outside the diffraction peak is studied within
different assumptions about the behavior of its real part. The integral
equation for the imaginary part is derived with the asymptotical expression for
the real part inserted in the unitarity condition. The conclusions about the
asymptotical approach to the black disk limit and possible zeros of the
imaginary part of the amplitude are obtained. Their relation to the present day
experiments is discussed.
