Consider the following premises. Susan is not reading a book. Robert is sleeping if and only if Joseph is a sailor. Susan is reading a book if and only if Joseph is a sailor. Can we infer the following from them? If we can, name the inference rule being used: Robert is sleeping.
 From the fact that Susan is reading a book if and only if Joseph is a sailor, and that Susan is not reading a book we can infer that Joseph is not a sailor via biconditional elimination. Finally, from the fact that Robert is sleeping if and only if Joseph is a sailor, and that Joseph is not a sailor we can infer that Robert is not sleeping via biconditional elimination, which contradicts that Robert is sleeping. Therefore, the answer is no.