  Given two arbitrary sequences of denoisers for block lengths tending to
infinity we ask if it is possible to construct a third sequence of denoisers
with an asymptotically vanishing (in block length) excess expected loss
relative to the best expected loss of the two given denoisers for all clean
channel input sequences. As in the setting of DUDE [1], which solves this
problem when the given denoisers are sliding block denoisers, the construction
is allowed to depend on the two given denoisers and the channel transition
probabilities. We show that under certain restrictions on the two given
denoisers the problem can be solved using a straightforward application of a
known loss estimation paradigm. We then show by way of a counter-example that
the loss estimation approach fails in the general case. Finally, we show that
for the binary symmetric channel, combining the loss estimation with a
randomization step leads to a solution to the stated problem under no
restrictions on the given denoisers.
