Consider the following premises. If Robert goes running, then John is playing a game. If James were a lawyer, then John is playing a game. If Robert goes running, then James is a lawyer. If John plays a game, then Robert is running. Can we infer the following from them? If we can, name the inference rule being used: James is a lawyer if and only if Robert is running.
 From the fact that if Robert goes running, then John is playing a game, and that if John plays a game, then Robert is running we can infer that Robert is running if and only if John is playing a game via biconditional introduction. From the fact that Robert is running if and only if John is playing a game we can infer that if John plays a game, then Robert is running via biconditional elimination. From the fact that if James were a lawyer, then John is playing a game, and that if John plays a game, then Robert is running we can infer that if James were a lawyer, then Robert is running via transitivity. Finally, from the fact that if James were a lawyer, then Robert is running, and that if Robert goes running, then James is a lawyer we can infer that James is a lawyer if and only if Robert is running via biconditional introduction. Therefore, the answer is yes.