stable cohomotopy





Special and general types

Special notions


Extra structure






The generalized cohomology theory which is represented by the sphere spectrum is also called stable cohomotopy, as it is the stable homotopy theory version of cohomotopy.

Equivalenty, it is the cohomolgical dual concept to stable homotopy homology theory.

By the Pontryagin-Thom theorem this is equivalently framed cobordism cohomology theory.


As algebraic K-theory over 𝔽 1\mathbb{F}_1

The following is known as the Barratt-Priddy-Quillen theorem:


(stable cohomotopy is K-theory of FinSet)

Let 𝒞=\mathcal{C} = FinSet be a skeleton of the category of finite sets, regarded as a permutative category. Then the K-theory of this permutative category

K(FinSet)𝕊 K(FinSet) \;\simeq\; \mathbb{S}

is represented by the sphere spectrum, hence is stable cohomotopy.

This is due to Barratt-Priddy 72 reproved in Segal 74, Prop. 3.5. See also Priddy 73, Glasman 13.


(stable cohomotopy as algebraic K-theory over the field with one element)

Notice that for FF a field, the K-theory of a permutative category of its category of modules FModF Mod is its algebraic K-theory KFK F (see this example)

KFK(FMod). K F \;\simeq\; K(F Mod) \,.

Now (pointed) finite sets may be regarded as the modules over the “field with one element𝔽 1\mathbb{F}_1 (see there):

𝔽 1Mod=FinSet */ \mathbb{F}_1 Mod \;=\; FinSet^{\ast/}

If this is understood, example says that stable cohomotopy is the algebraic K-theory of the field with one element:

𝕊K𝔽 1. \mathbb{S} \;\simeq\; K \mathbb{F}_1 \,.

This perspective is highlighted for instance in (Deitmar 06, p. 2, Guillot 06, Mahanta 17, Dundas-Goodwillie-McCarthy 13, II 1.2, Morava, Connes-Consani 16).

The perspective that the K-theory K𝔽 1K \mathbb{F}_1 over 𝔽 1\mathbb{F}_1 should be stable Cohomotopy has been highlighted in (Deitmar 06, p. 2, Guillot 06, Mahanta 17, Dundas-Goodwillie-McCarthy 13, II 1.2, Morava, Connes-Consani 16). Generalized to equivariant stable homotopy theory, the statement that equivariant K-theory K G𝔽 1 K_G \mathbb{F}_1 over 𝔽 1\mathbb{F}_1 should be equivariant stable Cohomotopy is discussed in Chu-Lorscheid-Santhanam 10, 5.3.

(equivariant) cohomologyrepresenting
equivariant cohomology
of the point *\ast
of classifying space BGB G
ordinary cohomology
HZBorel equivariance
H G (*)H (BG,)H^\bullet_G(\ast) \simeq H^\bullet(B G, \mathbb{Z})
complex K-theory
KUrepresentation ring
KU G(*)R (G)KU_G(\ast) \simeq R_{\mathbb{C}}(G)
Atiyah-Segal completion theorem
R(G)KU G(*)compl.KU G(*)^KU(BG)R(G) \simeq KU_G(\ast) \overset{ \text{compl.} }{\longrightarrow} \widehat {KU_G(\ast)} \simeq KU(B G)
complex cobordism cohomology
MUMU G(*)MU_G(\ast)completion theorem for complex cobordism cohomology
MU G(*)compl.MU G(*)^MU(BG)MU_G(\ast) \overset{ \text{compl.} }{\longrightarrow} \widehat {MU_G(\ast)} \simeq MU(B G)
algebraic K-theory
K𝔽 pK \mathbb{F}_prepresentation ring
(K𝔽 p) G(*)R p(G)(K \mathbb{F}_p)_G(\ast) \simeq R_p(G)
Rector completion theorem
R 𝔽 p(G)K(𝔽 p) G(*)compl.(K𝔽 p) G(*)^Rector 73K𝔽 p(BG)R_{\mathbb{F}_p}(G) \simeq K (\mathbb{F}_p)_G(\ast) \overset{ \text{compl.} }{\longrightarrow} \widehat {(K \mathbb{F}_p)_G(\ast)} \!\! \overset{\text{<a href="">Rector 73</a>}}{\simeq} \!\!\!\!\!\! K \mathbb{F}_p(B G)
stable cohomotopy
K𝔽 1Segal 74K \mathbb{F}_1 \overset{\text{<a href="stable cohomotopy#StableCohomotopyIsAlgebraicKTheoryOverFieldWithOneElement">Segal 74</a>}}{\simeq} SBurnside ring
𝕊 G(*)A(G)\mathbb{S}_G(\ast) \simeq A(G)
Segal-Carlsson completion theorem
A(G)Segal 71𝕊 G(*)compl.𝕊 G(*)^Carlsson 84𝕊(BG)A(G) \overset{\text{<a href="">Segal 71</a>}}{\simeq} \mathbb{S}_G(\ast) \overset{ \text{compl.} }{\longrightarrow} \widehat {\mathbb{S}_G(\ast)} \!\! \overset{\text{<a href="">Carlsson 84</a>}}{\simeq} \!\!\!\!\!\! \mathbb{S}(B G)

Kahn-Priddy theorem

The Kahn-Priddy theorem characterizes a comparison map between stable cohomotopy and cohomology with coefficients in the infinite real projective space P B/2\mathbb{R}P^\infty \simeq B \mathbb{Z}/2.

Boardman homomorphisms

Consider the unit morphism

𝕊H \mathbb{S} \longrightarrow H \mathbb{Z}

from the sphere spectrum to the Eilenberg-MacLane spectrum of the integers. For any topological space/spectrum postcomposition with this morphism induces Boardman homomorphisms of cohomology groups (in fact of commutative rings)

(1)b n:π n(X)H n(X,) b^n \;\colon\; \pi^n(X) \longrightarrow H^n(X, \mathbb{Z})

from the stable cohomotopy of XX in degree nn to its ordinary cohomology in degree nn.


(bounds on (co-)kernel of Boardman homomorphism from stable cohomotopy to integral cohomology)

If XX is a CW-spectrum which

  1. is (m1)(m-1)-(m-1)-connected

  2. of dimension dd \in \mathbb{N}


  1. the kernel of the Boardman homomorphism b nb^n (1) for

    mnd1 m \leq n\leq d -1

    is a ρ¯ dn\overline{\rho}_{d-n}-torsion group:

    ρ¯ dnker(b n)0 \overline{\rho}_{d-n} ker(b^n) \;\simeq\; 0
  2. the cokernel of the Boardman homomorphism b nb^n (1) for

    mnd2 m \leq n \leq d - 2

    is a ρ¯ dn1\overline{\rho}_{d-n-1}-torsion group:

    ρ¯ dn1coker(b n)0 \overline{\rho}_{d-n-1} coker(b^n) \;\simeq\; 0


ρ¯ i{1 | i1 j=1iexp(π j(𝕊)) | otherwise \overline{\rho}_{i} \;\coloneqq\; \left\{ \array{ 1 &\vert& i\leq 1 \\ \underoverset{j = 1}{i}{\prod} exp\left( \pi_j\left( \mathbb{S}\right) \right) &\vert& \text{otherwise} } \right.

is the product of the exponents of the stable homotopy groups of spheres in positive degree i\leq i.

(Arlettaz 04, theorem 1.2)

flavours of
cohomology theory
(full or rational)
equivariant cohomology
(full or rational)
non-abelian cohomologyCohomotopy
(full or rational)
equivariant Cohomotopy
twisted cohomology
(full or rational)
twisted Cohomotopytwisted equivariant Cohomotopy
stable cohomology
(full or rational)
stable Cohomotopyequivariant stable Cohomotopy


The basic concept appears in

The identification of stable cohomotopy with the K-theory of the permutative category of finite set is due to

see also

  • Stewart Priddy, Transfer, symmetric groups, and stable homotopy theory, in Higher K-Theories, Springer, Berlin, Heidelberg, 1973. 244-255 (pdf)

  • Saul Glasman, The multiplicative Barratt-Priddy-Quillen theorem and beyond, talk 2013 (pdf)

The resulting interpretation of stable cohomotopy as algebraic K-theory over the field with one element is amplified in the following texts:

see also

The Kahn-Priddy theorem is due to

The relation to β-rings is discussed in

  • E. Vallejo, Polynomial operations from Burnside rings to representation functors, J. Pure Appl. Algebra, 65 (1990), pp. 163–190.

  • E. Vallejo, Polynomial operations on stable cohomotopy, Manuscripta Math., 67 (1990), pp. 345–365

  • E. Vallejo, The free β-ring on one generator, J. Pure Appl. Algebra, 86 (1993), pp. 95–108.

  • Guillot 06

see also

  • Jack Morava, Rekha Santhanam, Power operations and absolute geometry (pdf)

Discussion of Boardman homomorphisms from stable cohomotopy is in

  • Dominique Arlettaz, The generalized Boardman homomorphisms, Central European Journal of Mathematics March 2004, Volume 2, Issue 1, pp 50-56

A lift of Seiberg-Witten invariants to classes in circle group-equivariant stable cohomotopy is discussed in

Last revised on December 1, 2019 at 14:14:36. See the history of this page for a list of all contributions to it.