  We prove that the law of a random walk $X_n$ is determined by the
one-dimensional distributions of $\max(X_n, 0)$ for $n = 1, 2, \ldots$, as
conjectured recently by Lo\"ic Chaumont and Ron Doney. Equivalently, the law of
$X_n$ is determined by its upward space-time Wiener-Hopf factor. Our methods
are complex-analytic.
