Comment by nrds

Comment by nrds 2 days ago

3 replies

The claims in this article, such as those suggesting recursion has something to do with the infinite, are all relative to the set-theoretic foundation. This is not essential.

In contrast, in the type theories behind proof assistants like Coq, Lean, and Agda, recursion is intimately tied to _finite_ structures. Instead of the vague "intersection of all sets such that" which we see in the article here, recursion is a well-defined computational process, and defined in a rather obvious way once you're familiar with the background.

GregarianChild a day ago

The "intersection of all sets such that" is not vague at all. It's perfectly formally defined in ZF* set theories. But it's impredicative. One of the guiding ideas behind type theories is to minimise impredicative constructions as much as possible. After all, impredicative definitions are circular ... Of course there is no free lunch and the power of impredicative constructions needs to be supplied in other ways in type theories ...

pengstrom a day ago

I think the fact that the initial _size_ of the recursion can be arbitrarily large is where infinity comes in. No matter your resources, there might be (must be?) a recision problem that's too large, that requires too many steps.

  • ysofunny a day ago

    I think "recursion" simpy said, allows for algorithms which end as much as "not ending algorithms".

    but in practice, an algorithm has gotta end, otherwise it's not very useful. I think some academics would go as far as insisting a function or process which never ends is not even a proper "algorithm"; but I digress.

    recursion does allow us to "reach the infinite"; however, philosophically, we can only ever grasp the finite.