Consider the following premises. Richard is working if and only if Jessica is running. If Richard works, then Jessica is running. Jessica is running or Richard is not working. Can we infer the following from them? If we can, name the inference rule being used: Jessica is running if and only if Richard is working.
 From the fact that Jessica is running or Richard is not working we can infer that if Richard works, then Jessica is running via rewriting. From the fact that Richard is working if and only if Jessica is running we can infer that if Jessica goes running, then Richard is working via biconditional elimination. From the fact that if Richard works, then Jessica is running, and that if Jessica goes running, then Richard is working we can infer that Richard is working if and only if Jessica is running via biconditional introduction. From the fact that Richard is working if and only if Jessica is running we can infer that if Jessica goes running, then Richard is working via biconditional elimination. Finally, from the fact that if Jessica goes running, then Richard is working, and that if Richard works, then Jessica is running we can infer that Jessica is running if and only if Richard is working via biconditional introduction. Therefore, the answer is yes.