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2 votes
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Can hypercompletion be an essential localization?

Jacob's answer to my last question actually answers this one too: if the hypercomplete objects are coreflective as well as reflective, and the coreflector is the same functor as the reflector, then of …
Mike Shulman's user avatar
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5 votes

Lex $\infty$-colimits

Probably not. Claim: Let $C$ be a small $(\infty,1)$-category with finite limits and colimits which admits an embedding $V:C\to E$ into a Grothendieck $(\infty,1)$-topos preserving finite limits and …
Mike Shulman's user avatar
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10 votes

Homotopy groups of spheres in a $(\infty, 1)$-topos

If it may be forgiven to resurrect a very old question, it's worth pointing out that these are not the "homotopy groups of spheres" that appear in synthetic homotopy theory / homotopy type theory. Th …
Mike Shulman's user avatar
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22 votes

Relation between topos and $\infty$-topos

Jacob's answer to your "for example" question is a good one, but let me be so bold as to try to address the general question. I think there are two different issues in play: the fact that the site of …
Mike Shulman's user avatar
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3 votes
Accepted

Base change in homotopy type theory

The answer to question 1 is yes. To see this, I think it's better to consider a "geometric sequent" to be of the form $$ (x:X), \phi(x) \vdash \psi(x) $$ since this avoids all mention of $\forall$ a …
Mike Shulman's user avatar
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6 votes
Accepted

Do stalks see epimorphism of stacks?

By definition (e.g. Remark 6.5.4.7 of Higher topos theory), an $n$-topos $\mathcal{E}$ has enough points if for every morphism $f:X\to Y$ in $\mathcal{E}$, whenever $p^*(f)$ is an equivalence for all …
Mike Shulman's user avatar
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22 votes

Reflection principle vs universes

I'd like to mention something that I think hasn't been pointed out yet. The original question began with In set-theoretic language, one fixes some strongly inaccessible cardinal $\kappa$... This imp …
Mike Shulman's user avatar
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14 votes

$\infty$-categorical interpretation of type theory

More generally, the issue with such interpretation is that substitution in type theory is interpreted by pullback in category theory, and substitution in ordinary type theory preserves all type-theore …
Mike Shulman's user avatar
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5 votes
Accepted

When the global section functor is a Cartesian fibration?

In fact I believe something quite general can be said: if $p:C\to D$ is any functor that preserves finite limits, then it is a Street fibration if and only if it has a fully faithful right adjoint. A …
Mike Shulman's user avatar
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9 votes
Accepted

How to formulate the univalence axiom without universes?

One possibility along these lines is large eliminations for higher inductive types. For instance, here is a large elimination rule for the higher inductive interval type $\mathsf{I}$ with $0,1:\maths …
Mike Shulman's user avatar
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