Hi,

playing with my code to build Metamath proofs from ITP programs, I
generated this proof of the theorem asserting that each group where all
elements have order 2 is commutative:


https://github.com/giomasce/set.mm/commit/6b64e8068b1c1c82d2fb714c42ae2615bee80094

I thought anyone having a fetish for monster Metamath proofs might like
it. You can also find the HTML rendering here (25 MB, be careful!):

  https://people.debian.org/~gio/monsterord2com.html

This is the description, with some additional explanation on why it is
so big and weird:

---
A monster theorem, proving that a group where every element has order 2
(i.e., every element multiplied by itself is the identity) is commutative.

The proof is automatically generated: the original problem is fed as a
First-Order Formula to Prover9, whose proof is processed with GAPT to
convert it to Natural Deduction style. The program mmpp is finally used
to express the proof in the Metamath language. Since the original
theorem is not completely trivial itself and each conversion step adds a
good amount of bookkeeping code, the final result is huge and hardly
readable by any human being.

The statement itself is littered with artifacts due to the automatic
conversion from a First Order Formula. The class 𝐴 is the group
identity and the class 𝐵 (depending on variables 𝑡 and 𝑒) is the
group operation. Explicit substitution is used both in the statement and
in the proof in order to bridge the gap between FOF and Metamath's
treating of predicates' and functors' arguments: while in First Order
Formulae arguments are explicit and order-based, in Metamath they are
implicit and name-based. A conspicuous amount of bookkeeping must be put
in place to handle this discrepancy.
---

BTW, the proof generated by mmpp is uncompressed. Compressing with with
metamath.exe took a few good minutes.

Giovanni.
-- 
Giovanni Mascellani <[email protected]>
Postdoc researcher - Université Libre de Bruxelles

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