Reflected and diffracted waves have different nature and role in the applied seismics. Diffractions itself can be classified in both real seismic and hypothetical diffractions. The real seismic diffractions are seismic waves which are scattered on small heterogeneities in the subsurface or diffracted at the edges and tips, and recorded as the diffracted part of the whole wavefield. To image objects beyond the classical Rayleigh limit, it is indispensable to use real seismic diffractions.The hypothetical diffractions are mathematical constructions resulting from Huygens principle which helps...