Consider the following premises. Robert is writing a letter if and only if Charles is sleeping. If Charles sleeps, then Robert is a server. Can we infer the following from them? The fact that Robert writes a letter does not imply that Robert is a server.
 From the fact that Robert is writing a letter if and only if Charles is sleeping we can infer that if Robert writes a letter, then Charles is sleeping. Finally, from the fact that if Robert writes a letter, then Charles is sleeping, and that if Charles sleeps, then Robert is a server we can infer that if Robert writes a letter, then Robert is a server, which contradicts that The fact that Robert writes a letter does not imply that Robert is a server. Therefore, the answer is no.