This is nice work Stanislas, thank you.

On Friday, July 3, 2020 at 5:09:55 AM UTC-4, Stanislas Polu wrote:

- `1re` uses more axioms but is much simpler (how do we feel about 
> that given the comment there?). 
>

A problem with this particular proof is that it uses df-1, which has the 
tag "(New usage is discouraged.)".

Let me explain a little about how the complex numbers are introduced.  Our 
overall goal in set.mm is to show mathematics that follows from the ZFC 
axioms.  For complex numbers, we construct a model (a set of axioms stated 
as $p statements) starting from ZFC axioms.  We then restate these derived 
axioms ($p statements) as actual axioms ($a statements) in order to (1) 
make the complex number development independent from the construction (so 
that alternate models could in principle be "plugged in") and (2) make it 
easier to see what complex number axioms are needed for a particular 
complex number theorem.  So, for example, we derive ax1cn in the model 
part, then restate that theorem as axiom ax-1cn.  (To help ensure we're not 
cheating by introducing new axioms beyond ZFC, the 'verify markup' command 
in metamath.exe checks that each ax-* $a statement exactly matches an 
earlier $p statement with the "-" removed, if such a $p statement exists.)

To help prevent the accidental usage of the complex number construction 
when we later use complex numbers, we have "(New usage is discouraged.)" in 
every statement in the development of the complex number model.  df-1 is 
one such statement, since it might change if we used a different complex 
number construction.

For our metamath.exe and mmj2 proof assistants, the string "(New usage is 
discouraged.)" in a comment tells the proof assistant not to consider that 
statement for use in a proof being developed.  In addition, the Travis run 
that is done after each pull request checks that the usage of statements 
with "(New usage is discouraged.)" didn't change as a result of the PR 
(unless it was done intentionally and the user has supplied a regenerated 
"discouraged" file as part of the PR).

I would recommend that the OpenAI assistant check statement descriptions 
for the string "(New usage is discouraged.)" and avoid considering them for 
use in proofs.  (The metamath.exe command 'write source set.mm /rewrap' 
currently prevents this string from being broken across lines, but I'm not 
sure we want to guarantee that, nor can we guarantee the '/rewrap' command 
was run.  But for a quick and dirty check you can assume it's not broken 
across lines and refine it later with a TODO.)

Norm

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