  Interdependencies between experimental spectra, representing line or plane
projections of electronic densities, are derived from their consistency and
symmetry conditions. Some additional relations for plane projections are
obtained by treating them as line projections of line projections.
  The knowledge of these dependencies can be utilised both for an improvement
of experimental data and for a verification of various techniques used for
correcting e.g. two-dimensional (or one-dimensional) angular correlation of
annihilation radiation spectra and Compton scattering profiles.
