Consider the following premises. Sarah is playing a game if and only if William is a lawyer. Sarah is playing a game. Can we infer the following from them? William is not a lawyer.
 From the fact that Sarah is playing a game if and only if William is a lawyer we can infer that if Sarah plays a game, then William is a lawyer. Finally, from the fact that if Sarah plays a game, then William is a lawyer, and that Sarah is playing a game we can infer that William is a lawyer, which contradicts that William is not a lawyer. Therefore, the answer is no.