Combeferre frowns, and then smiles. "If it's a logic puzzle, I know how to solve it. We ask either guard this question: If I asked the other guard whether you would tell the truth or lie, what would he say? And you see, if we're talking to the liar, he will say the other guard will say he--the first guard, that is--will tell the truth. If we're talking to the truthful one, he will say the other guard will say he will lie."

Combeferre beams. Surely this is the simplest and most explicable way out of their dilemma.