Consider the following premises. Elisabeth is not a janitor. If John works, then it is sunny. Elisabeth is a janitor if and only if Charles is an artist. It is sunny if and only if Charles is an artist. Can we infer the following from them? If we can, name the inference rule being used: John is not working.
 From the fact that Elisabeth is a janitor if and only if Charles is an artist, and that Elisabeth is not a janitor we can infer that Charles is not an artist via biconditional elimination. From the fact that it is sunny if and only if Charles is an artist, and that Charles is not an artist we can infer that it is not sunny via biconditional elimination. Finally, from the fact that if John works, then it is sunny, and that it is not sunny we can infer that John is not working via modus tollens. Therefore, the answer is yes.