  Suppose that attached to each site z in Z is a coin with bias theta(z), and
only finitely many of these coins have non-zero bias. Allow a simple random
walker to generate observations by tossing, at each move, the coin attached to
its current position. Then we can determine the biases {theta(z) : z in Z},
using only the outcomes of these coin tosses and no information about the path
of the random walker, up to a shift and reflection of Z. This generalizes a
result of Harris and Keane.
