When I was first learning quantum mechanics, I would occasionally feel compelled to lodge a complaint on behalf of common sense. My physics teacher would fix me with his twinkling gaze and intone, “Truth is stranger than fiction.” He was right, and not only about the behavior of elementary particles. Umberto Eco’s latest fiction, “The Prague Cemetery,” is choreographed by a truth that is itself so strange a novelist need hardly expand on it to produce a wondrous tale. Eco forthrightly explains that all his major characters but one are historical figures; but a reader unaware of how close to the truth Eco is hewing might be inclined to award him more points for inventiveness than he earns. This is not to say that Eco doesn’t earn points for inventiveness, nor that a novel can’t succeed on other grounds. It is just to say that sometimes truth is stranger than fiction