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Prove tz7.48lem without ax-8 #3199
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The way ax-8 is avoided is basically bj-ax8 so idk if this is an actual improvement
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Can you tell where bj-ax8 is used? Metamath.exe doesn't show me:
If true that would be odd since bj-ax8 is in a mathbox, and I didn't have
/INCLUDE_MATHBOXES
activated, so it would be a bug of the minimizer.Also is it even possible to depend from a statement that appears after the main one? I'm new here, so there might be something that I'm missing.
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I mean that eleq1w is more general than elequ1 but doesn't use ax-8, due to df-clel being "too powerful" in its current state
So the way ax-8 is "saved" here is equivalent to the way it is saved in bj-ax8.
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That's interesting. If df-clel is too powerful, it seems dangerous to leave it like that, shouldn't it have a
New usage is discouraged
label on it?However in this case df-clel was already used in
fvres
andordtri3
, so technically it wasn't introduced as a new dependency fortz7.48lem
. The final outcome is still a clear loss.There was a problem hiding this comment.
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I originally approved but I did not have @icecream17's sharp eye about axiom dependency!
I think this is pending @icecream17's answer and so I will continue to hold merging for now.
For reference, there were mailing list exchanges between Norm and @benjub about ax-8. I think ultimately, Norm preferred to keep the actual axioms as near to the literature as possible, and so Benoît's suggestions were kept in his mathbox.
@avekens @jkingdon @digama0 don't hesitate to step in if you have an opinion!
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I was under the impression that the mailing group discussion settled the point: Norm said he preferred to keep the current axioms, and have the alternative solution in a mathbox, @benjub agreed to do so, and that's the situation we have until now.
Did I understand that correctly? I'm also not diving much into these discussions.
We could reopen that discussion, though.
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A problem with changing the definition now is that currently cleljust2 would add ax-10 ax-12 ax-13 which obscures their actual usages. These axioms would be removed by the new definition of substitution df-ssb.
So if wanting to introduce ax-8 to df-clel, then the choices are either wait until df-ssb is merged or add ax-8 to df-clel in some arbitrary fashion (like with dfcleq and ax-9)
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In case someone isn't following the recent additions in the metamath-knife repo, a discussion about
df-clel
df-clab
df-cleq
was brought up in this PR which adds a definition checker.There was a problem hiding this comment.
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Perhaps one could introduce dfclel which arbitrarily introduces ax-8. This would be a quick solution.
I say this now because based on #3250 + #3262 it seems this would unintuitively affect $j statements.Edit: Wait, elequ2 doesn't use ax-8. nvm
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The ideal of "arbitrarily" introducing ax-8 is, I guess, similar to what we did with ax-9 in https://us.metamath.org/mpeuni/dfcleq.html . But I suppose that sort of thing sidesteps the question of what
the real status (axiom or definition) of
df-clel
df-clab
anddf-cleq
is.