Consider the following premises. Michael is reading a book if and only if Linda is writing a letter. If it is sunny, then Linda is not writing a letter. Michael is not reading a book. If Linda doesn't write a letter, then it is sunny. Can we infer the following from them? If we can, name the inference rule being used: It is sunny.
 From the fact that Michael is reading a book if and only if Linda is writing a letter, and that Michael is not reading a book we can infer that Linda is not writing a letter via biconditional elimination. From the fact that if it is sunny, then Linda is not writing a letter, and that if Linda doesn't write a letter, then it is sunny we can infer that it is sunny if and only if Linda is not writing a letter via biconditional introduction. From the fact that it is sunny if and only if Linda is not writing a letter we can infer that if Linda doesn't write a letter, then it is sunny via biconditional elimination. Finally, from the fact that if Linda doesn't write a letter, then it is sunny, and that Linda is not writing a letter we can infer that it is sunny via modus ponens. Therefore, the answer is yes.