One of you also pointed out the following correction:
Begin forwarded message:
> Would I be correct in assuming that the preamble to Problem 2 should
> also have
>
> $\tilde{f}(x) = \tilde{s}_n$
> and
> $\tilde{s}_k = \tilde{s}_{k-1} \oplus x_k$
>
> instead of what's written there?