Consider the following premises. It is not windy. Charles is a server if and only if Richard is writing a letter. Charles is a server if and only if it is windy. Can we infer the following from them? If we can, name the inference rule being used: Richard is not writing a letter.
 From the fact that Charles is a server if and only if it is windy we can infer that if Charles were a server, then it is windy via biconditional elimination. From the fact that if Charles were a server, then it is windy, and that it is not windy we can infer that Charles is not a server via modus tollens. Finally, from the fact that Charles is a server if and only if Richard is writing a letter, and that Charles is not a server we can infer that Richard is not writing a letter via biconditional elimination. Therefore, the answer is yes.