" (Incidentally, although it is no part of the reason for declining the unblock request, I will mention another point. I am intrigued to know how a proof of non-existence of something can possibly be constructive. If I wish to prove that something exists, then I may or may not do so in a way that shows how to construct it. If, however, something does not exist, then I can't possibly show how to construct it. Either I have grossly misunderstood something, or you don't actually know what it means to describe a proof as ""constructive"".)"