  It is argued that within the correct treatment of analytical properties of
the transition amplitudes, in particular, the second order pole structure,
characteristic for the $n - \bar n$ transition in nuclei, the "infrared
divergences" discussed in some papers, do not appear. Explicit calculation with
the help of diagram technique shows that the neutron-antineutron oscillations
are strongly suppressed within a deuteron, as well as within arbitrary nucleus,
in comparison with the oscillations in vacuum.
