You absolutely need to read the lean proof firstly to assess the correctness of the proposition it is proving (ie in this case that it is actually proving or otherwise the smoothness of navier-stokes in R^3 and not something else) and secondly to determine whether the proof is “honest” in the sense given here https://lean-lang.org/doc/reference/latest/ValidatingProofs/
This is all you need to read and understand for Anthropic's FLT formalization:
import Mathlib
import Theorems.Thm_fermat_last_theorem
/-- Solution side: the same statement, binder for binder, proved by this tree's `fermat_last_theorem`. -/
theorem FLT_for_comparator (n : ℕ) (hn : 3 ≤ n) (a b c : ℕ) (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) :
a ^ n + b ^ n ≠ c ^ n :=
fermat_last_theorem n hn a b c ha hb hc
/-- Mathlib's named proposition, by the one-line bridge from the elementary statement
(the bridge is restated inline so that this file depends only on `Theorems.Thm_fermat_last_theorem`). -/
theorem FLT_mathlib_for_comparator : FermatLastTheorem :=
fun n hn a b c ha hb hc => fermat_last_theorem n hn a b c (Nat.pos_of_ne_zero ha) (Nat.pos_of_ne_zero hb) (Nat.pos_of_ne_zero hc)
First of all, that is Fermat's Last Theorem, not Navier-Stokes.
Second of all, you did not read the link.
> In particular, we use honest when the goal is to create a valid proof. This allows for mistakes and bugs in proofs and meta-code (tactics, attributes, commands, etc.), but not for code that clearly only serves to circumvent the system (such as using the debug.skipKernelTC).
Given that AI has autonomously found proofs of `False` in Lean and other proof assistants, it is far from impossible that such a circumvention could be present somewhere in 13 million lines.
Perhaps you did not understand the Fermat theorem proof announcement/repo or the link. The 13 million lines did not use any external, possibly not honest libraries, as the proof eventually only used the fundamental axioms. So for the Fermat theorem formalization, no open open questions remain.
If we read the link, it has a section called Gold Standard: comparator and external checkers, and comparator is how OpenAI has gone about checking their lean proofs.
> Can you elaborate on what constitutes a vacuous proof?
Trivially, a proof that relies on a bug in Lean. Less trivially, a proof that is technically true but about something trivial and does not, in fact, prove what it claims to have proven.
It can happen when the proof process ends up with universal implication that holds trivially. Then you end it with something like Forall x, x is empty -> P(x).
This statement is 100% logically coherent internally. But it also doesn't matter because we know that 1 does not equal 3 so this proof is completely pointless. I could also say 3 == 5 and it would still be logically sound but completely useless information.
Are you proving for some arbitrary definition of == that isn't what we commonly consider the definition? How is it logically coherent? You mean only in the sense that you say it is and you haven't provided any rules to disprove it?
No the definition of == is the regular definition; it's just a deductive reasoning statement. Since the first part of the statement is never true, it doesn't matter what the second part of it says. Of course, like he said, that makes the statement have no value.
E.g. “If it’s raining, the sidewalk is wet.” That statement holds if it’s not raining or the sidewalk is wet.
This is a common occurrence in mathematics, where someone might not be able to unconditionally prove Y, but they can under the condition X. Later, another mathematician might build on this by proving X, thereby transitively proving Y. (Or conversely, they might unconditionally disprove Y, thereby disproving X.)
Many hard problems are answered this way.
For example, Fermat’s Last Theorem was proven assuming the Taniyama-Shimura-Weil Conjecture, then Wiles proved the conjecture.
Thousands of theorems rely on the the unproven Reinmann Hypothesis, which is why it’s so interesting to mathematicians.
But if your precondition is “stupid,” your proof is stupid.
If you have a software engineering background, it's like how semantic versioning is bollocks.
Semantic versioning describes the following idealized setup:
- you have an interface you expose (a contract, and thus a contract signature)
- you do not change the contract signature -> patch version bump
- you do change it but in a non-breaking way (e.g. additively) -> minor version bump
- you do change it but in a breaking way (e.g. mutatively or destructively) -> major version bump
One would expect then that since interface signatures are statically derivable, semantic version tags can be auto-assigned. And indeed, in lots of shops that's exactly what happens (in my opinion, correctly).
The problem with this is that it comes with a lot more smoke than fire. The interface having no changes or non-breaking changes doesn't mean the actual code behind those interfaces is not going to cause a breakage. It literally is just about the interface itself.
And so unless you encode absolutely everything about the semantics your implementation actually observes into the interface, which is what the semver specification asks you to do so as their sleight of hand, this means the interface will be a leaky abstraction. Which means that external software interfacing with yours may observe behavior that is beyond the purview of semantic versioning. Which means that they do. Which means that they absolutely can and will break, and your package managers' fancy version constraint syntax exists to make such fun events happen.
The way this is usually handled then is:
- you live with the pain: acknowledge the limitations of semver, accept you've been duped, and just give in
- you have human release managers assign versions manually, based on whole program and whole system semantics (with the human overhead and error that entails), falsely claiming that what you're doing is still semver
- you switch to a less deceptive versioning scheme, like calendar versioning; as a bonus, you now no longer have to pretend that your entire application somehow only has a single unified interface
This mirrors the Lean statement and Lean proof situation. The statement is like an interface, and the proof is like the implementation behind that interface. The way the proof is derived may expose semantic gaps in the statement itself, and (ab)use them to obtain the logical consistency certificate. Hence, a vacuous proof, and hence why this is not statically assertable to be not the case. It is part of the challenge in asserting that the statement was correctly formalized in the first place: you need to manually identify whether the way the consistency was achieved is actually meaningful, or just a formalization gap.
Which really makes me wonder about the actual value proposition of Lean then, but alas...
When I first started playing with lean I accidentally defined a group in such a way that it was reduced to triviality. It had one object in it, so everything in the group was trivially equal to everything else. It was not the group that I was trying to prove something about, but the proof went through.
It was too easy, so I double checked my definitions, but it is quite easy to do something like that. And Claude does things like that quite frequently.
I am going through the exercise right now of trying to get Claude to formalize a published paper and it is a _struggle_ to get it not to take shortcuts or prove approximations of the paper’s theorems and then tell you it’s done.
While I agree with that, my layman's understanding is that the whole purpose of Lean is that once you agree that the program does "do what it says it does", all the intermediate steps can be verified with a compilation.
That is, verifying a proof in English was a painstaking, years long process in the past as independent mathematicians looked for holes in the steps connecting the logic. When the proof is written in Lean, all of that work goes away. My point is that if OpenAI publishes the Lean code (not sure if they already did), verification should take weeks not years.
