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Part of higher category theory that for instance in Algebraic Topology enables us to capture finer homotopic distinctions. As in say Eilenberg-Maclane spaces.

3 votes
Accepted

Algebras over the trivial $\infty$-operad

One can avoid relative Kan extensions, but since this calculation hinges on the fact that $\mathcal{C}^\otimes$ is right Kan extended from $\{\langle 1 \rangle\} \to \mathrm{Triv}^\otimes$, I suspect …
daniel gratzer's user avatar
3 votes

Monomorphisms of diagrams in an $\infty$-category

(Assuming $\mathcal{C}$ is finitely complete for convenience) A partial answer at least: For the first, $\eta$ is an monomorphism iff its diagonal map $\delta : f \to f \times_g f$ is an isomorphism. …
daniel gratzer's user avatar
2 votes
Accepted

Cofinal maps from posets (HTT, 4.2.3.16)

[Rephrasing my comment as an answer] While I cannot speak for the actual proof, two points are worth noting. First, a similar construction appears in Kerodon (https://kerodon.net/tag/02QA) but there ( …
daniel gratzer's user avatar
2 votes
Accepted

Connectedness of truncated version of cosimplicial indexing category

I don't believe the first claim is true, but I can give a somewhat formal argument for the connectivity of $\Delta_{\le n} \times_{\Delta} \Delta_{/m}$. Let us write $u$ for the inclusion $\Delta_{\le …
daniel gratzer's user avatar
4 votes
Accepted

Limits of infinity categories and mapping spaces

Yes. To see this, let us make the preliminary observation that it suffices to prove that this holds for products and pullbacks since we can decompose a general limit into these two special cases. Let …
daniel gratzer's user avatar
8 votes
Accepted

Functoriality of infinite suspension spectrum functor on infinity groupoids!

I'm not sure if this counts as a direct way, but a more practical way to show functoriality at the level of $\infty$-categories is to not construct $\Sigma^\infty$ as a functor directly, but instead s …
daniel gratzer's user avatar
5 votes
Accepted

How to prove $\text{Map}_C(X,Y)$ is a grouplike commutative monoid object of the $\infty$-ca...

A reference is Corollary II.17 of the lecture notes on algebraic and hermitian K theory by Fabian Hebestreit (typeset copy by Ferdinand Wagner available here). The argument is relatively short, so I h …
daniel gratzer's user avatar