Consider the following premises. If Robert reads a book, then David is a scientist. If Susan sleeps, then Richard is happy. It is late if and only if Robert is reading a book. It is late if and only if Richard is happy. Can we infer the following from them? If we can, name the inference rule being used: If Susan sleeps, then David is a scientist.
 From the fact that it is late if and only if Robert is reading a book we can infer that if it is late, then Robert is reading a book via biconditional elimination. From the fact that if it is late, then Robert is reading a book, and that if Robert reads a book, then David is a scientist we can infer that if it is late, then David is a scientist via transitivity. From the fact that it is late if and only if Richard is happy we can infer that if Richard were happy, then it is late via biconditional elimination. From the fact that if Richard were happy, then it is late, and that if it is late, then David is a scientist we can infer that if Richard were happy, then David is a scientist via transitivity. Finally, from the fact that if Susan sleeps, then Richard is happy, and that if Richard were happy, then David is a scientist we can infer that if Susan sleeps, then David is a scientist via transitivity. Therefore, the answer is yes.