That's the joke/trick, it's basically begging the question. You can out a cheater by asking a question of the form: Which is true, (A and A->B) or (A and A->C)

That's the joke/trick, it's basically begging the question. You can out a cheater by asking a question of the form: Which is true, (A and A->B) or (A and A->C)? A cheater will fret over whether B or C is true, while someone who did the work will probably immediately identify that A is false and that the question is misleadingly worded.