Oh, I see. It&#x27;s an element in the empty set, which is indeed  very troubling for constructive logic. Well, they&#x27;re both troubling in different ways. Your example is troubling from a pure mathematical soundness perspective, and mine is from the &quot;physical&quot;[1] applicability of the model.<p>[1]: The relationship between classical math and computation is in some ways like that of math and physics, except that physics requires empirical corroboration, while computation is a kind of a new &quot;physical&quot; math that incorporates time. In either case the result can be the same: the math could be sound but useless. In physics it may contradict observation; in computation it can allow unbounded (even if not infinite) complexity.