Consider the following premises. s -> p. u <-> s. p -> s. Can we infer ~(p -> u) from them?
 From p -> s, s -> p we can infer p <-> s. From u <-> s we can infer s -> u. From p <-> s we can infer p -> s. Finally, from p -> s, s -> u we can infer p -> u, which contradicts ~(p -> u). Therefore, the answer is no.