Suppose that federal courts did not use the Mottley rule; instead, they upheld jurisdiction under 28 U.S.C. 1331 if either the plaintiff's complaint or the defendant's answer raised an issue of federal law. The Mottleys bring suit in federal court, demanding specific performance of their contract. You represent the railroad, which is considering raising several defenses to the Mottleys' claim, some based in federal law and some in state law. If you wanted to avoid federal court, what would you advise the railroad to do in answering the complaint?