User blog comment:Kyodaisuu/Pseudo Rayo's number/@comment-180.214.233.28-20141218163823/@comment-1605058-20141218170353

There is more to well-definedness than that. For example, when I say "largest positive integer" there is absolutely no ambiguity about the concepts I use, yet this is not a well-defined number, for a simple reason that it doesn't exist.