  A problem of amplitude reconstruction in terms of the given angular
distribution is considered. Solution of this problem is not unique. A class of
amplitudes, correspondent to one and the same angular distribution, forms a
region in projection onto a finite set of spherical harmonics. An explicit
parametrization of a boundary of the region is obtained. A shape of the region
of ambiguities is studied in particular example. A scheme of partial-wave
analysis, which describes all solutions in the limits of the region, is
proposed.
