MO editors' lounge

Martin Sleziak

11:03 AM

specific-question No top-level tag: Composition of bibundles

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I am reading Orbifolds as stacks? Given Lie groupoids $\mathcal{G}$ and $\mathcal{H}$ there is a notion of what is called a bibundle from $\mathcal{G}$ to $\mathcal{H}$ which is supposed to be a ageneralized notion of a morphism of Lie groupoids. (rough) Definition : A bibundle is a groupoid pri...

@DavidRoberts I see you've bumped the answer recently. As the answerer, perhaps you'd be able to suggest a suitable top-level tag.

I guess it was bumped because of this:

I just wanted to point out a small error in the second paragraph in case anyone else gets confused like I did. Namely that $\mathbf{B}G$ should not act trivially on $u(H)$, it should act via $\phi$. This is implicit in the next paragraph though, so no harm, no foul :) — Connor Grady Nov 27 at 4:06

@Connor thanks! I should fix it. — David Roberts ♦ Nov 27 at 5:46

Martin Sleziak

12:34 PM

specific-question I guess that if the paln is to keep the tag consistency, it would be suitable here: Con(PA) via non-well-foundedness? At the same time, there was a suggestion that this tag should be removed:

Nov 24 at 10:23, by YCor

@MartinSleziak I guess consistency should be removed. It is a quite broad tag in set theory. I think that tags that are in principle suitable for hundred/thousands of question but are only used for a few rare ones, are not useful.

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Q: Con(PA) via non-well-foundedness?

Lumsdaine made the following interesting comment: if Con(PA) fails in a non-standard model, it means it contains a “proof of non-standard length” of a contradiction from PA. With a little work, one can externalise that to some non-well-founded “proof tree”, which has at each node a possibly-non...

lo.logic theories-of-arithmetic

David Roberts

10:39 PM

@MartinSleziak done!

And, yes, your deduction as to the cause is correct.

Martin Sleziak

11:24 PM

Thanks!

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Q: Composition of bibundles

I am reading Orbifolds as stacks? Given Lie groupoids $\mathcal{G}$ and $\mathcal{H}$ there is a notion of what is called a bibundle from $\mathcal{G}$ to $\mathcal{H}$ which is supposed to be a ageneralized notion of a morphism of Lie groupoids. (rough) Definition : A bibundle is a groupoid pri...

dg.differential-geometry ct.category-theory stacks lie-groupoids

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