  In the framework of field approach with finite time interval the particle
oscillations in a medium are considered. The absorption in a final states do
not lead to dramatic suppression of ab-transitions. Also we touch on the
problem of infrared singularities. The approach under study is infrared-free.
It is shown that "correction" published recently [A.Gal, Phys. Rev. C61 (2000)
028201] is clearly wrong.
