Since every simplicial group is in particular a Kan complex with group structure, hence an ∞-groupoid with group structure, hence an ∞-group, the Dold-Kan correspondence says that connective chain complexes are a model for certain abelian ∞-groups, thus the correspondence interpolates between homological algebra and general simplicial homotopy theory. (This is part of the cosmic cube of higher category theory). The relevance of this is that chain complexes are typically easier to handle: all the tools of homological algebra apply. In fact, the functor that identifies simplicial abelian groups with their corresponding chain complexes – the normalized chains functor – does precisely this: it normalizes an abelian group by discarding irrelevant information and constructing a smaller and less redundant model for it.

There are various variants and generalizations of the Dold-Kan correspondence. These are discussed further below.

Statement (abelian case)

Let AA be an abelian category.

We say a chain complex in AA is connective if it is concentrated in non-negative degree. The full subcategory

Ch • +(A)↪Ch •(A) Ch^+_\bullet(A) \hookrightarrow Ch_\bullet(A)

of connective chain complexes is naturally identified with the category of ℕ\mathbb{N}-graded chain complexes.

Equivalence of categories

\begin{theorem} (Dold–Puppe) For AA an abelian category there is an equivalence of categories

N:A Δ op→←Ch • +(A):Γ N \;\colon\; A^{\Delta^{op}} \stackrel{\leftarrow}{\to} Ch_\bullet^+(A) \;\colon\; \Gamma

between

the category of simplicial objects in AA;
the category of connective chain complexes in AA;

where

NN is the normalized chains complex/normalized Moore complex functor.

\end{theorem}

(Dold 58, Kan 58, Dold-Puppe 61).

\begin{theorem} (Kan) \linebreak For the case that AA is the category Ab of abelian groups, the functors NN and Γ\Gamma are nerve and realization with respect to the cosimplicial chain complex

ℤ[−]:Δ⟶Ch +(Ab) \mathbb{Z}[-] \;\colon\; \Delta \longrightarrow Ch_+(Ab)

that sends the standard nn-simplex to the normalized Moore complex of the free simplicial abelian group F ℤ(Δ n)F_{\mathbb{Z}}(\Delta^n) on the simplicial set Δ n\Delta^n, i.e.

Γ(V):[k]↦Hom Ch • +(Ab)(N(ℤ(Δ[k])),V). \Gamma(V) \;\colon\; [k] \mapsto Hom_{Ch_\bullet^+(Ab)} \Big( N \big( \mathbb{Z}(\Delta[k]) \big), \, V \Big) \,.

\end{theorem}

This is due to (Kan 58).

More explicitly:

\begin{proposition}\label{ExplicitFormOfGamma}

For V∈Ch • +V \in Ch_\bullet^+ the simplicial abelian group Γ(V)\Gamma(V) is in degree n∈ℕn \in \mathbb{N} given by

Γ(V) n=⨁ [n]↠[k]V k \Gamma(V)_n \;=\; \bigoplus_{[n] \twoheadrightarrow [k]} V_k

and for θ:[m]→[n]\theta : [m] \to [n] a morphism in Δ\Delta the corresponding map Γ(V) n→Γ(V) m\Gamma(V)_n \to \Gamma(V)_m

θ *:⨁ [n]↠[k]V k→⨁ [m]↠[r]V r \theta^* : \bigoplus_{[n] \twoheadrightarrow [k]} V_k \to \bigoplus_{[m] \twoheadrightarrow [r]} V_r

is given on the direct summand indexed by some σ:[n]→[k]\sigma \colon [n] \to [k] by the composite

V k→d *V s↪⨁ [m]↠[r]V r, V_k \overset{d^*}{\to} V_s \hookrightarrow \bigoplus_{[m] \twoheadrightarrow [r]} V_r \,,

where

[m]↠t[s]↪d[k] [m] \overset{t}{\twoheadrightarrow} [s] \overset{d}{\hookrightarrow} [k]

is the epi-mono factorization of the composite [m]→θ[n]→σ[k][m] \stackrel{\theta}{\to} [n] \stackrel{\sigma}{\to} [k].

\end{proposition}

In these terms (Prop. \ref{ExplicitFormOfGamma}) we have:

Proposition

The natural isomorphism ΓN→Id\Gamma N \to Id is given on A∈sAb Δ opA \in sAb^{\Delta^{op}} by the map

⨁ [n]↠[k](NA) k→A n \bigoplus_{[n] \twoheadrightarrow [k]} (N A)_k \to A_n

which on the direct summand indexed by σ:[n]→[k]\sigma \colon [n] \to [k] is the composite

NA k↪A k→σ *A n. N A_k \hookrightarrow A_k \stackrel{\sigma^*}{\to} A_n \,.
The natural isomorphism Id→NΓId \to N \Gamma is on a chain complex VV given by the composite of the projection

V→C(Γ(V))→C(Γ(C))/D(Γ(V)) V \to C(\Gamma(V)) \to C(\Gamma(C))/D(\Gamma(V))

with the inverse

C(Γ(V))/D(Γ(V))→NΓ(V) C(\Gamma(V))/D(\Gamma(V)) \to N \Gamma(V)

of

NΓ(V)↪C(Γ(V))→C(Γ(V))/D(Γ(V)) N \Gamma(V) \hookrightarrow C(\Gamma(V)) \to C(\Gamma(V))/D(\Gamma(V))

(which is indeed an isomorphism, as discussed at Moore complex).

This is spelled out in Goerss & Jardine, prop. 2.2 in section III.2

Proposition

With the explicit choice for ΓN→≃Id\Gamma N \stackrel{\simeq}{\to} Id as above we have that Γ\Gamma and NN form an adjoint equivalence (Γ⊣N)(\Gamma \dashv N)

This is for instance (Weibel, exercise 8.4.2).

Quillen equivalence of model categories

Both Ch • +(A)Ch_\bullet^+(A) and A Δ opA^{\Delta^{op}} are categories with weak equivalences in an standard way:

the weak equivalences of simplicial abelian groups are the weak homotopy equivalences of the underlying Kan complexes, hence morphisms that induce isomorphisms on all simplicial homotopy groups;
the weak equivalences of chain complexes are the quasi-isomorphisms: the morphisms that induces isomorphisms on all chain homology groups.

The structures of categories with weak equivalences have standard refinements to model category structures:

the projective model structure on chain complexes Ch •Ch_\bullet has as fibrations the chain maps that are surjections in each positive degree;
the model structure on simplicial abelian groups has as fibrations those whose underlying morphisms in sSet are fibrations with respect to the classical model structure on simplicial sets (hence: Kan fibrations).

Proposition

Both

(N⊣Γ):Ch • +→Γ←NsAb (N \dashv \Gamma) \;\colon\; Ch_\bullet^+ \stackrel{\overset{N}{\leftarrow}}{\underset{\Gamma}{\to}} sAb

as well as

(Γ⊣N):sAb→N←ΓCh • + (\Gamma \dashv N) \;\colon\; sAb \stackrel{\overset{\Gamma}{\leftarrow}}{\underset{N}{\to}} Ch_\bullet^+

are Quillen equivalences with respect to these model structures.

This is due to Quillen 67, Section II.4 item 5, see also Schwede-Shipley 03, section 4.1, p.17, Jardine 03, Lemma 1.5).

Statement (additive case)

The Dold-Kan correspondence generalizes from Ab to any abelian category (Lurie, §1.2.3) and fruther to additive categories for which all retractions come from direct sums, as is the case for triangulated categories (Lurie, §1.2.4).

Statement (general nonabelian case)

Globular and cubical version

There are versions of the Dold-Kan correspondence for other geometric shapes for higher structures than the simplex, also for the globe and the cube.

\begin{theorem} (globular Dold-Kan correspondence)\linebreak

Write Ab for the category of abelian groups. (Could be any additive category with kernels for the following to be true). Then the following categories of structures internal to AbAb are equivalent.

The category of chain complexes (in non-negative degree).
The category of crossed complexes.
The category of cubical sets with connection on a cubical set.
The category of cubical strict ∞-groupoids.
The category of globular strict ∞-groupoids.

\end{theorem}

A proof with references to the rich literature can be found for instance in

Ronnie Brown, Philip Higgins, Rafael Sivera, Nonabelian Algebraic Topology

see the section Cubical Dold-Kan theorem.

This version of the Dold-Kan theorem reproduces the simplicial Dold-Kan theorem after application of the omega-nerve, i.e. the simplicial Dold-Kan correspondence factors through the globular one via the ω\omega-nerve.

Presentation of strict groupal ∞\infty-groupoids

It was mentioned above that the standard simplicial Dold-Kan correspondence Ch •(Ab)→←sAbCh_\bullet(Ab) \stackrel{\leftarrow}{\to} sAb may be understood as identifying strictly abelian strict ∞-groupoids among all ∞-groupoids. This statement is also surveyed and put into a larger context at cosmic cube of higher category theory.

We now give a formal version of this statement, following an observation by Richard Garner. A different but closely analogous sequence of arguments to the same extent is also in the book

Ronnie Brown, Philip Higgins, Rafael Sivera, Nonabelian Algebraic Topology, European Math. Soc. Tracts in Mathematics 15, 2011.

see Dold-Kan map and omega-nerve.

Definition

Write

(L⊣R):Ch •(Ab) +→←Str∞Cat(Ab)→←Str∞Cat(Set) (L \dashv R) : Ch_\bullet(Ab)^+ \stackrel{\leftarrow}{\to} Str \infty Cat(Ab) \stackrel{\leftarrow}{\to} Str \infty Cat(Set)

for the adjunction obtained by composing the globular Dold-Kan correspondence with the forgetful functor which forgets the abelian group structure on a strict ∞\infty-category in the image of the globular/cubical Dold-Kan map.

Proposition

The functor

C •:Δ→Ch • + C_\bullet : \Delta \to Ch_\bullet^+

which sends a simplex to its (normalized) chain complex factors as

C •:Δ→𝒪Str∞Cat→LCh • +, C_\bullet : \Delta \stackrel{\mathcal{O}}{\to} Str \infty Cat \stackrel{L}{\to} Ch_\bullet^+ \,,

where the cosimplicial strict ∞\infty-category 𝒪\mathcal{O} is the oriental functor.

This is a remark by Richard Garner posted here.

Proof

Use that 𝒪(n)\mathcal{O}(n) is the free strict ∞\infty-category on a computad.

Observe that LL sends a strict ω\omega-category XX to the chain complex obtained from the abelian reflexive globular set X×mathbZX \times \mathb{Z}. In particular the value on the nn-globe is the chain complex

ℤ→ℤ⊕ℤ→ℤ⊕ℤ→⋯→ℤ⊕ℤ \mathbb{Z} \to \mathbb{Z}\oplus\mathbb{Z} \to \mathbb{Z}\oplus\mathbb{Z} \to \cdots \to \mathbb{Z}\oplus\mathbb{Z}

with (n+1)(n+1) terms and differential given by x↦(x,−x)x \mapsto (x, -x) in each dimension.

Moreover, the value of LL on the boundary of the nn-globe is the chain complex obtained from this by removing the uppermost copy of ℤ\mathbb{Z}.

Given a computad CC, the associated abelian chain complex LCL C has for (LC) n(L C)_n the free abelian group on the set of generating nn-cells of CC, and differential given by ∂x=∑ jt j−∑ is i\partial x = \sum_j t_j - \sum_i s_i, where {s i}\{s_i\} and {t i}\{t_i\} are the sets of source- and or target-cells, respectively. A glance at Ross Street’s presentation of the orientals shows that L(𝒪(n))=C •(Δ[n])L(\mathcal{O}(n)) = C_\bullet(\Delta[n]).

Corollary

The simplicial Dold-Kan map

Hom(C •Δ[n],−):Ch •+→sSet Hom(C_\bullet \Delta[n], -) : Ch_\bullet + \to sSet

factors as the identification of chain complexes with strictly abelian strict ∞\infty-groupoids, followed by the functor that forgets the abelian structure and then followed by the omega-nerve operation that embeds strict ∞\infty-groupoids into all ∞\infty-groupoids.

Proof

Use the above adjunction and proposition to write for K •K_\bullet a chain complex

Hom Ch •(C •Δ[n],K)=Hom Ch •(L𝒪(n),K)=Hom Str∞Cat(𝒪(n),RK)=N(RK) n. Hom_{Ch_\bullet}(C_\bullet \Delta[n], K) = Hom_{Ch_\bullet}(L \mathcal{O}(n), K) = Hom_{Str \infty Cat}(\mathcal{O}(n), R K) = N (R K)_n \,.

Remark The alternative construction in Nonabelian Algebraic Topology factors also versions of the nonabelian Dold-Kan correspondence through the ω\omega-nerve.

Non-abelian forms of the Dold-Kan correspondence.

Perhaps the ‘ultimate’ form of a ‘classical’ Dold–Kan result is by Pilar Carrasco, who identified the extra structure on chain complexes of groups in order that they be Moore complexes of simplicial groups. Dominique Bourn has a general form of this result for his semi-abelian categories. His results provide a neat categorical gloss on the theorem.

Dominique Bourn’s formulation is very pretty. The Moore complex functor is monadic when the basic category is semi-Abelian (Th. 1.4. p.113 in Bourn2007 below). Of course for simplicial groups, the monad on chain complexes of groups gives the hypercrossed complexes of Carrasco and Cegarra, but here they fall out from the theory. On the down side there is apparently no full analysis as yet of the actual form of this monad.

Gary Nan Tie showed that a certain full subcategory of filtered systems of hypergroupoids of rank n is equivalent to the following three categories, n-groupoids, n-simplicial T-complexes and n-crossed complexes, and in doing so proved a non-abelian Dold-Kan theorem for crossed complexes:

A Dold-Kan theorem for crossed complexes, Journal of Pure and Applied Algebra, Volume 56, Issue 2, 1989, Pages 177-194, ISSN 0022-4049, https://doi.org/10.1016/0022-4049(89)90143-6

Iterated W̄ and T-groupoids, Journal of Pure and Applied Algebra, Volume 56, Issue 2, 1989, Pages 195-209, ISSN 0022-4049, https://doi.org/10.1016/0022-4049(89)90144-8

Stable Dold-Kan correspondence

The Dold-Kan correspondence stabilizes to identify unbounded chain complexes with the category of stably simplicial abelian groups. The latter are closely related to combinatorial spectra of Daniel Kan and can be defined as stably simplicial objects in the category of abelian groups. More precisely, we have the following definitions.

Definition

The category of stable simplices has integer numbers as objects. Given two objects kk and ll, the set of morphisms from kk to ll is the set of order-preserving maps hh from the set of natural numbers to itself such that h(n)=n+l−kh(n)=n+l-k for all but a finite number of nn. Morphisms are composed by composing the corresponding maps.

Definition

A stably simplicial abelian group is a presheaf FF of abelian groups on the category of stable simplices such that for any integer kk every element xx of F(k)F(k) belongs to the kernels of all but a finite number of degeneracy maps. Morphisms of stably simplicial abelian groups are morphisms of presheaves.

The following theorem was established in 1963 by Daniel Kan in his paper “Semisimplicial spectra” (see Proposition 5.8):

Theorem

The category of unbounded chain complexes is equivalent to the category of stably simplicial abelian groups, with equivalences being given by the same functors as in the unstable Dold-Kan correspondence, but appropriately extended to the above categories.

Similarly to the unstable case, the above categories, when interpreted as ∞-categories, are also equivalent to the ∞-category of module spectra over the Eilenberg-MacLane ring spectrum of the integers. For more see at stable Dold-Kan correspondence.

Generalizations and variants

There are various variants, generalizations and enhancements of the Dold–Kan correspondence.

The monoidal Dold-Kan correspondence relates simplicial algebras with dg-algebras.
In rational homotopy theory, Quillen proved and used an analogous statement for Lie algebras: a Quillen equivalence between the reduced rational dg-Lie algebras and reduced rational simplicial Lie algebras:

D. Quillen, Rational homotopy theory , Ann. Math. 90 (1969), 204–265.
The statement of the Dold–Kan correspondence generalizes to sheaves with values in the respective categories and this way from ∞Grpd to more general (∞,1)(\infty,1)-topoi:

For XX be a site, let Sh(X,sAb)Sh(X, sAb) be the category of simplicial abelian sheaves – i.e. simplicial sheaves which take values in simplicial abelian groups – and let Sh(X,Ch +(Ab))Sh(X, Ch_+(Ab)) be the category of sheaves on SS with values in non-negatively graded chain complexes of abelian groups. The normalized chain complex extends objectwise to a functor

Sh(X,sAb)→≃Sh(X,Ch +(Ab)) Sh(X,sAb) \stackrel{\simeq}{\to} Sh(X, Ch_+(Ab))

which is an equivalence of categories. Moreover, both these categories are naturally categories with weak equivalences: the weak equivalences in Sh(X,sAb)Sh(X, sAb) are the stalkwise weak equivalences of simplicial sets and the weak equivalences in Sh(X,Ch +(Ab))Sh(X, Ch_+(Ab)) are the quasi-isomorphisms. The normalized chain complex functor preserves these weak equivalences. This sheaf version of the Dold–Kan correspondence allows to understand abelian sheaf cohomology as a special case of nonabelian cohomology.

See page 9,10 of
- K. Brown, Abstract Homotopy Theory and Generalized Sheaf Cohomology
There is a version of the Dold–Kan correspondence in the context of (∞,1)(\infty,1)-categories:

let CC be a stable (∞,1)-category. Then the (∞,1)(\infty,1)-categories of non-negatively graded complexes in CC is equivalent to the (∞,1)(\infty,1)-category of simplicial objects in CC

Fun(N(ℤ ≥0),C)≃Fun(N(Δ) op,C). Fun(N(\mathbb{Z}_{\geq 0}), C) \simeq Fun(N(\Delta)^{op}, C) \,.

This is infinity-Dold-Kan correspondence is theorem 12.8, p. 50 of
- Jacob Lurie, Stable ∞-Categories
There is a version of the Dold–Kan correspondence with simplicial sets generalized to dendroidal sets. This is described in
- Javier Gutiérrez, Andor Lukacs, Ittay Weiss, Dold-Kan correspondence for dendroidal abelian groups (arXiv)
Various functor categories of interest in stable homotopy theory and homological stability are involved in generalized Dold-Kan equivalences. These equivalences have been studied independently by several authors, including Pirashvili , Słomińska, Helmstutler, and Lack and Street
There is a categorification of the correspondence, categorified Dold-Kan correspondence (Dyckerhoff17)

Applications

Eilenberg-MacLane objects

The Dold-Kan correspondence gives a convenient construction of Eilenberg-MacLane objects in simplicial groups.

Proposition

For AA an abelian group write A[−n]A[-n] for the chain complex concentrated on AA in degree nn.

The simplicial abelian group Γ(A[−n])\Gamma (A[-n]) is an Eilenberg-MacLane object K(A,n)K(A,n).

And conversely, every such Eilenberg-MacLane object in simplicial abelian groups is related by an ∞-anafunctor-equivalence to a Γ(A[−n])\Gamma(A[-n]).

Looping and delooping

The Dold-Kan correspondence provides a convenient way to describe formation of loop space objects and delooping for anything in the image of Ξ:Ch •→sSet\Xi : Ch_\bullet \to sSet:

by the basic fact that the homotopy groups of Ξ(V •)\Xi(V_\bullet) are the homology groups of V •V_\bullet, looping and delooping simply corresponds to shifting chain complexes up or down in degree.

But the relation is also strongly coherent: it respects the standard delooping functor W¯:sGrp→sSet\bar W : sGrp \to sSet for simplicial groups (see there and at looping and delooping) (notice that restricted to simplicial abelian groups this produces simplicial abelian groups W¯:sAbGrp→sAbGrp\bar W : sAbGrp \to sAbGrp):

Proposition

There is a natural isomorphism

NW¯G≃(NG)[−1]N \bar W G \simeq (N G)[-1]

natural in G∈sAbGrpdG \in sAbGrpd.

This appears for instance as (Goerss & Jardine, remark III.5.6) or around (Jardine, theorem 4.57).

Abelian sheaf cohomology in nonabelian cohomology

Composed with the forgetful functor sAb→sSetsAb \to sSet the Dold-Kan correspondence presents certain simplicial sets by chain complexes. Since this is entirely functorial, it prolongs to a functor from chain complexes of (pre)sheaves on any site SS, to simplicial presheaves

Γ:[S op,Ch • +(ab)]→[S op,sSet]\Gamma : [S^{op}, Ch_\bullet^+(ab)] \to [S^{op}, sSet]

If [S op,sSet][S^{op}, sSet] is equipped with the projective model structure on simplicial presheaves it models the (∞,1)-sheaf (∞,1)-topos on SS. The derived hom-spaces compute general nonabelian cohomology.

If the coefficient objects come from sheaves of chain complexes along Γ\Gamma, this cohomology restricts to ordinary abelian sheaf cohomology. See there for more details.

Computational aspects

One may view the (monoidal) Dold-Kan correspondence as a relation between a well-behaved theory (simplicial/higher methods) that work in any characteristic but is very abstract and mainly suited to the proof of abstract theorems, and a more computational theory (strict structures in dg-modules) that are particularly well adapted to computations. The relation between these two (symmetric monoidal) theories may only be properly used with characteristic 0 coefficients. This remark is very naive and basic, but certainly at the center of computational implementations of abstract homotopical methods.

Dold-Kan correspondence
monoidal Dold-Kan correspondence, Eilenberg-Zilber/Alexander-Whitney deformation retraction
operadic Dold-Kan correspondence
infinity-Dold-Kan correspondence
stable Dold-Kan correspondence
categorified Dold-Kan correspondence

References

The original articles:

Albrecht Dold, Homology of symmetric products and other functors of complexes, Annals of Mathematics Second Series 68 1 (Jul., 1958) 54-80 (jstor:1970043)

considers the correspondence for categories of modules, and

Albrecht Dold, Dieter Puppe, Homologie nicht-additiver Funktoren. Anwendungen, Annales de l’institut Fourier 11 (1961) 201-312 [[eudml:73776]]

generalizes the result to arbitrary abelian categories.

The general expression of the correspondence in terms of nerve and realization is due to

Daniel Kan, Functors involving c.s.s complexes, Transactions of the American Mathematical Society, 87 2 (March 1958) 330-346 (jstor:1993103).

This remarkable article introduces not just the abstract nerve and realization form of the Dold-Kan correspondence, but introduces the general notion of nerve and realization and in fact the general notion of what is now called Kan extension.

The Dold-Kan correspondence as a Quillen equivalence between the model structure on simplicial abelian groups and the projective model structure on chain complexes is due to

Daniel Quillen, Section II.4 item 5 in: Homotopical Algebra, Lecture Notes in Mathematics 43, Springer 1967(doi:10.1007/BFb0097438)

A textbook reference for the ordinary Dold-Kan correspondence:

Similar material is in section 4.6 of

J. F. Jardine, Generalized etale cohomology theories Modern Birkhäuser Classics, (1991)

Interpretation via model categories:

Stefan Schwede, Brooke Shipley, Equivalences of monoidal model categories, Algebr. Geom. Topol. 3 (2003) 287-334 [[arXiv:math.AT/0209342](http://arxiv.org/abs/math.AT/0209342), euclid:euclid.agt/1513882376]
J. F. Jardine, Lemma 1.5 in: Presheaves of chain complexes, K-theory 30.4 (2003): 365-420 (pdf, pdf)

Further review:

Jacob Lurie, The Dold-Kan correspondence, Section 2.5.6 in Kerodon [[tag 00QQ](https://kerodon.net/tag/00QQ)]

Discussion in the generality of abelian categories (and further generalization, in section 1.2.4 to additive categories in which retractions come from direct sums):

Jacob Lurie, section 1.2.3 of: Higher Algebra

The relation between strict ∞-groupoids and crossed complexes is in

R. Brown and P.J. Higgins, The equivalence of ∞\infty-groupoids and crossed complexes, Cahiers de Topologie et Géométrie Différentielle Catégoriques, 22 no. 4 (1981), p. 371–386 (pdf)

P. 59 of

R. Brown, Groupoids and crossed objects in algebraic topology, Homology, Homotopy and Applications, 1 (1999) 1-78.

gives seven equivalent categories with the equivalences all expressing nonabelian versions of the Dold–Kan correspondence. One of these is given in

Ashley, N., Simplicial T-complexes and crossed complexes: a nonabelian version of a theorem of Dold and Kan. University of Wales PhD Thesis, (1978); Dissertationes Math. (Rozprawy Mat.) 265 (1988) 1–61.

The relation of these with the abelian version is given in

Brown, R. and Higgins, P. J., Cubical abelian groups with connections are equivalent to chain complexes. Homology Homotopy Appl. 5 (1) (2003) 49–52.

The paper

G. J. Ellis , andR. Steiner Higher-dimensional crossed modules and the homotopy groups of (n+1)(n+1)}-ads.J. Pure Appl. Algebra_ 46 (2-3) (1987) 117–136.

should also be seen as of Dold-Kan type. The homotopical applications considerably generalise results on the Blakers-Massey theorem.

Dold-Kan correspondence (changes) in nLab

Context

Homological algebra

Homotopy theory

Contents

Idea

Statement (abelian case)

Equivalence of categories

Proposition

Proposition

Quillen equivalence of model categories

Proposition

Statement (additive case)

Statement (general nonabelian case)

Globular and cubical version

Presentation of strict groupal ∞\infty-groupoids

Definition

Proposition

Proof

Corollary

Proof

Non-abelian forms of the Dold-Kan correspondence.

Stable Dold-Kan correspondence

Definition

Definition

Theorem

Generalizations and variants

Applications

Eilenberg-MacLane objects

Proposition

Looping and delooping

Proposition

Abelian sheaf cohomology in nonabelian cohomology

Computational aspects

References