Questions tagged [simplicial-stuff]
For questions about simplicial sets, simplicial (co)algebras and simplicial objects in other categories; geometric realization, Dold-Kan correspondence, simplicial resolutions etc.
778
questions
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About definition of homotopy colimit of Kan and Bousfield
In Bousfield and Kan's book"Homotopy Limits, Completions and Localizations",they define homotopy direct limit for system of pointed simplicial sets(Ch XII S2 2.1 P327), while they define ...
4
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0
answers
127
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Example of non reduced representable functor from simplicial rings
Let $\text{sCR}_k$ be the over category of simplicial commuative rings (so objects are maps $R \to k$), where $k$ is the simplicial field generated by a non-derived field of the same name. Let $R \in \...
6
votes
1
answer
332
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Elementary proof of the exactness of Čech complex associated to a hypercovering ("Illusie's Conjecture")
Let $\mathcal{E}$ be a sheaf of abelian groups on a topological space (or a site). For an open covering $\mathfrak{U} = (U_i)_i$, it is well known that the augmented Čech complex $0 \to \mathcal{E} \...
3
votes
1
answer
186
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Derived Category of strictly simplicial algebraic space vs. systems of objects in the derived categories
Let $X_{\bullet}^+$ be a strictly simplicial algebraic space and for a morphism $\delta:[m]\to[n]$ in $\Delta^+$, let $\delta:X_n\to X_m$ also denote the associated map (by abuse of notation). Then ...
2
votes
1
answer
276
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question about notation in HTT of J.Lurie
In page 27 in HTT of J.Lurie, the expression
$$\text{Map}_S(X,Y):=Y^X\times_{S^X}\{\phi\}\in \text{Set}_\Delta$$
appears for simplicial set $X,Y,S$ in Warning 1.2.2.2. However, I couldn't understand ...
6
votes
1
answer
374
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What are some "good" examples of Kan simplicial manifolds?
According to the definition 1.1 of the paper Kan Replacement of simplicial manifolds by Chenchang Zhu https://arxiv.org/pdf/0812.4150.pdf,
A Kan simplicial manifold is a simplicial manifold $X$ such ...
5
votes
2
answers
425
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Regular or h-regular CW-complex structure for the Poincaré homology sphere
I am looking for a regular (the characteristic maps of the cells are homeomorphisms) or h-regular (the characteristic maps of the cells are homotopy equivalences) CW-complex structure for the Poincaré ...
12
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1
answer
293
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Can one show corbordism invariance of the Crane-Yetter state-sum using simplicial methods / are there 'Pachner-like' moves for cobordisms?
Let $\mathcal{C}$ denote some Unitary Braided Modular Fusion Category. It is well known that the Crane-Yetter state-sum, $Z_{CY}(\bullet|\mathcal{C})$ is an oriented-cobordism invariant. In other ...
4
votes
1
answer
273
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A cochain complex using degeneracy maps
In constructing singular homology for a topological space, the boundary operator for the singular chain complex is given as an alternating sum of face maps. The degeneracy maps seem to be discarded in ...
5
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1
answer
132
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Why is this condition necessary for the existence of a transferred simplicial model structure?
In chapter II of Goerss and Jardine's text on simplicial homotopy theory, they give a general theorem, Theorem 6.8, for transfer of simplicial model structures across a simplicial adjunction. This ...
4
votes
1
answer
213
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Computing homotopy colimit of a space with free $S^1$-action
Context. I am trying to understand the argument in B.4 of Thomas Nikolaus, Peter Scholze, On topological cyclic homology, arXiv:1707.01799 (on p147).
I am still lost. But from Maxime's helpful ...
7
votes
0
answers
167
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Stabilisation of crossed modules?
D. Conduché has introduced a notion of a stable crossed module ("Modules croisés généralisés de longueur 2", JPAA 34 (1984) pp155–178, doi:10.1016/0022-4049(84)90034-3, Def. 3.1).
Is there a ...
5
votes
0
answers
299
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Čech nerve $C(U)$ corresponds to $BG$ in same manner as a hypercover $\mathcal{H}(U)$ to
We can via the bar construction canonically associate to a monoid $A$ the nerve $N(B A)$, a simplicial set with $N(\mathbf{B}A)_k := \times^{k+1} A $ and canonical face maps and degeneracy maps ...
3
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0
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119
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does geometric realization factor through an endofunctor?
Does the functor of geometric realization of a simplicial set as a topological space,
factor through an endofunctor of the category of simplicial topological spaces which does something non-trivial (...
2
votes
0
answers
115
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when is the pullback along the shift (decalage) morphism a direct product, in sSets
What is the meaning of the following condition on a morphism in sSets
or simplicial topological spaces:
a morphism becomes a direct product after the pullback along
the shift(decalage) morphism ?
...
7
votes
0
answers
190
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2d TQFTs with values in simplicial sets and Reedy categories
Let $Cob$ be the category such that
$Obj(Cob)$ is $\emptyset\sqcup\mathbb{N}$, with $n$ seen as the union of $(n+1)$ circles numbered from $0$ to $n$,
morphisms are (homeomorphism classes of ...
2
votes
1
answer
116
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Kan replacement of finite $\mathbb{Q}$-type simplicial set
Sorry if this question is maybe a bit basic, but it is on a rather specialized topic so I think it is more appropriate for MO than SE.
Suppose that $X$ is a simplicial set that has finitely many
non-...
4
votes
1
answer
207
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Higher homotopy groups of Joyal fibrant replacements of 2-coskeletal simplicial sets
Suppose $X$ is a 2-coskeletal simplicial set (meaning $X^{Δ^k}→X^{∂Δ^k}$ is an isomorphism for all $k≥3$).
What is the easiest example of $X$ such that the Joyal fibrant replacement $Y$ of $X$
is not ...
3
votes
0
answers
64
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Homotopy limits of section spaces
Let $\mathcal{U}$ be an open cover of a topological space $B$. As we see, for example in this question, the associated Cech diagram $B_{\mathcal{U}}$ constitutes a simplicial space with the weak ...
4
votes
1
answer
343
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Contractibility of the category of cosimplicial resolutions
Let $\gamma : \mathcal{C} \to \mathcal{M}$ be a functor and define a cosimplicial resoultion of $\gamma$ as a functor $\Gamma: \mathcal{C} \to \mathcal{M}^{\Delta}$ such that
$\Gamma C$ is Reedy ...
2
votes
1
answer
243
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What is the difference between Path $\infty$-groupoid and Smooth Fundamental $\infty$-groupoid of a smooth space?
A couple of days back I asked a question Is there a Geometric/Smooth version of Homotopy Hypothesis using the path $\infty$-Groupoid of a Smooth Space? in MO about the existence of a possible Smooth/...
4
votes
1
answer
344
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Homotopy descent and cohomology
I've been reading "Structured Brown representability via concordance" by D.Pavlov (https://dmitripavlov.org/concordance.pdf) and I'm strugeling with a point and was wondering if someone ...
4
votes
2
answers
344
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Non-degenerate simplexes in a Kan complex
I have the following question on simplicial sets:
a non-constant Kan complex has a non-degenerate simplex in every sufficiently large simplicial degree?
It's Exercise 8.2.3 (p. 262) of Charles ...
3
votes
0
answers
159
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Homotopy Kan extensions, formally coherent functors and derived Schlessinger criterion
Let $k$ be a finite field. Denote by $discArt_k$ the category of Artinian rings with residue field $k$ and $Art_k$ the category of Artinian simplicial rings. Consider a functor $\mathcal{F}:disArt_k\...
7
votes
1
answer
160
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Locally minimal simplicial categories
Given a (fibrant) simplicially enriched category $\mathcal{C}$, I'm interested in the possibility of replacing it with a weakly equivalent one (in Bergner model structure) such that all the mapping ...
2
votes
1
answer
285
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Meaning of "combinatorial data"
I saw several times that often some data describing certain
algebraic objects,
eg the set of cells of a simplical complex
or a Cech cycle of a chosen coving of a variety
are called "combinatorial ...
7
votes
1
answer
404
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Visualize (co)sketeton of a simplicial set (geometrical intuition)
I want to understand if there is an intuition approchable with
most possible 'elementary geometrical' knowledge for
$n$-(co)skeleta of simplicial sets?
Formally sketleton & coskeleton functions ...
4
votes
1
answer
257
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($1$-)pullbacks of Kan complexes
Ultimately, I'm trying to figure out whether or not the full subcategory in $\mathbf{sSet}$ spanned by Kan complexes is finitely complete (as a $1$-category).
Since fibrations are stable under ...
1
vote
0
answers
188
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Schlessinger criterion and finiteness of tangent space
Schlessinger's criterion allows us to study whether or not a functor $\mathcal{F}:C_{\Lambda}\rightarrow \text{Set}$ from the category of local Artin $\Lambda$-algebras to sets is representable. One ...
5
votes
1
answer
450
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Computation on homotopy colimit cocomplete triangulated categories
I have a couple of questions about dealing with homotopy (co)limits cocomplete triangulated categories.
Question I:The first one concerns a comment by Peter Arndt in this discussion about derived ...
7
votes
1
answer
199
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Groupoid completion of a topological category vs its homotopy category?
Given a category $\mathcal{C}$ enriched in spaces, we can take the nerve (a simplicial space) and then geometric realization to get a space $B\mathcal{C}$. If we view spaces as $\infty$-groupoids, ...
4
votes
0
answers
375
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Etale sites for stacks
Let $X$ be an algebraic stack, let $U\to X$ be a smooth cover by an algebraic space. In this setting, we have the big étale site of $X$ (if $X$ is a stack over a scheme $S$, this is the restriction of ...
5
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0
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119
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The homotopy type of the simplicial space obtained by free adding degeneracies to a semi-simplicial space
Let $\text{sTop},\text{ssTop}$ denote the categories of simplicial, semi-simplicial spaces respectively. There is a functor $E:\text{ssTop}\rightarrow \text{sTop}$ that is left adjoint to the ...
0
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0
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56
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Questions about a structure related to simplicial complexes
While researching some superficially unrelated theory, a structure similar to the one described below presented itself to me. I'm having trouble with identifying what's the structure name. It seems to ...
5
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0
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119
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Simplicial matrices and the nerves of weak n-categories II, III, and IV
Duskin introduced his nerve functor (see the nLab or Kerodon) in the paper
Duskin, John W. Simplicial matrices and the nerves of weak n-categories I: nerves of bicategories. [Link].
While three ...
3
votes
1
answer
98
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Multi-simplicial generalization of $\Gamma$-spaces
Is there a generalization of Segal's theorem that the inclusion of $X_1$ into $\Omega|X_*|$ is a weak equivalence for a $\Gamma$-space $X_*$ if $X_1$ is group like? Specifically, I am looking for a ...
1
vote
1
answer
349
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How do you prove that the category of weak equivalences of sSet is accessible?
I am trying to prove that the category of simplicial sets is a combinatorial model category by using Proposition A.2.6.15 of Lurie's book, and this requires proving that the weak equivalences are ...
10
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0
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282
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A certain semi-simplicial space
I would like to understand whether the following construction has been studied. Let me model the pointed sphere as $S^n = I^n / \partial I^n$, and let $\Omega^n (-) := map((I^n, \partial I^n), (-, *))$...
6
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0
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129
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Any comparison between the category of cubes and its opposite?
To model topological spaces combinatorially, one can use simplicial sets -- or cubical sets. Simplicial sets are defined as presheaves on the simplex category $\Delta$, the category of non-empty ...
8
votes
2
answers
830
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Reference for homotopy colimit = total complex
I'm looking for a reference for the following fact:
take a simplicial chain complex $ X:\Delta^{op}\to Ch_{\geq 0}(\mathcal A)$ for $\mathcal A$ a nice abelian category (say, cocomplete with enough ...
6
votes
3
answers
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What is the geometric realization of the the nerve of a fundamental groupoid of a space?
It can be easily seen that there exists a functor $F:Top \rightarrow Grpd$ from the category of topological spaces to the category of groupoids defined as follows:
Obj: $X \mapsto \pi_{\leq 1}(X)$, ...
7
votes
1
answer
378
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The $\infty$-category of natural transformations as an end
Let $\mathcal{C}$ be an $\infty$-category viewed as a fibrant scaled simplicial set with all 2-simplices thin and let $\mathfrak{C}\!at_{\infty}$ be the $\infty$-bicategory of $\infty$-categories. A ...
4
votes
1
answer
521
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What is the notion of a group object and its action in a 2-category?
It is well known that a group object in a category $C$ (with terminal object $1$ and such that any two objects of $C$ have a product) is defined as an object $G$ in $C$ with the following morphisms:
$...
1
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0
answers
145
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What is the meaning of lifting property? and some question in $\infty$-category
When I learn model category, the important compute tool is the lifting property between $(\operatorname{Cof}, \operatorname{Fib} \cap W)$ and $(\operatorname{Cof} \cap W, \operatorname{Fib}) $, where $...
5
votes
1
answer
125
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Considering each half of factorization of weak equivalence separately
I have been working through the proof of Theorem 3.4.1 in the article https://arxiv.org/pdf/1211.2851.pdf (pages 35-6), but there is one technical detail still unclear to me.
Specifically, we have ...
2
votes
0
answers
78
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Pro-trivial cosimplicial tower of spaces
Let $\{X^\bullet_s\}$ be a cosimplicial tower of spaces. In other words, for each fixed "tower degree" n, we have a (let's assume Reedy fibrant) cosimplicial space $X^\bullet_n$, and for each fixed ...
1
vote
0
answers
69
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Simplicial differential graded algebra and a filtration
Let $A$ be a simplicial differential algebra, i.e. for each $n \in \mathbb{N}$ a differential graded algebra $(A_n,d_n)$ and for each weakly increasing map $f \colon [n] \to [m]$ a morphism $f_* \...
1
vote
1
answer
171
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Showing that a certain simplicial set has levelwise small cardinality
My question concerns Section 2 of the article "The Simplicial Model of Univalent Foundations (after Voevodsky)" (https://arxiv.org/pdf/1211.2851.pdf).
Let $\alpha$ be a strongly inaccessible cardinal....
4
votes
1
answer
120
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On equivalences of cartesian fibrations
Let $p:X^{\natural} \to S$, $q:Y^{\natural} \to S$ be two cartesian fibrations of simplicial sets (where the marking is given by cartesian edges) and assume that we are given an equivalence of ...
2
votes
0
answers
157
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Is every simplicial spectrum equivalent to an abelian group simplicial spectrum?
I wonder if every simplicial $S^1$-spectrum stable equivalent to an abelian group simplicial $S^1$-spectrum? It seems that I could use the stable Dold-Kan on the heart and use Postnikov towers?