  The problem of velocity selection for reaction fronts has been intensively
investigated, leading to the successful marginal stability approach for
propagation into an unstable state. Because the front velocity is controlled by
the leading edge which perforce has low density, it is interesting to study the
role that finite particle number fluctuations have on this picture. Here, we
use the well-known mapping of discrete Markov processes to stochastic
differential equations and focus on the front velocity in the simple $A+A
\stackrel{\leftarrow}{\to} A$ system. Our results are consistent with a recent
(heuristic) proposal that $v_{MS} - v \sim {1\over \ln^2 {N}}$.
