  Increase of the cut-off value in the high order harmonics generation process
is demonstrated for a special case of the driving field composed of several
harmonics of a given frequency. It is shown that a moderate, of the order of
20%, increase in the cut-off value can be achieved. This result possibly
constitutes an upper limit for the increase in the cut-off value, attainable
for a class of the waveforms considered in the paper.
