Finite generation for the $K(n)$ -local sphere

Claims every homotopy group of the K(n)-local sphere is finitely generated over the p-adic integers.

1 paper September 24, 2026 Explained by AI

The K(n)-local sphere isolates one chromatic layer of the stable homotopy groups of spheres. Its rational part was already known, but its torsion part could in principle be infinitely large in some degree. Hovey and Strickland asked whether each homotopy group is finitely generated over the p-adic integers. This paper claims yes, at every prime and height. It gives no uniform bound on the number of generators.

First step

1999

Mark Hovey and Neil Strickland, Morava K-theories and localisation, Problem 16.2

Significance

Major

It answers a standard finiteness question in chromatic homotopy theory at every height, where earlier proofs covered height one and height two for large primes.

Trust

Claimed, not checked

Field

Topology

1 paper

The explanation

Start with a group that is small in one sense but large in another. Take infinitely many copies of the integers mod p, side by side. Every element gives zero when multiplied by p. Allowing fractions kills the whole group, so its rational part is zero. Yet no finite list of elements generates itSource 1. So knowing the rational part says nothing about the size of the torsion.

The K(n)-local sphere is a piece of stable homotopy theory that isolates one chromatic height n. Its homotopy groups live in every integer degree, including negative onesSource 2. Barthel, Schlank, Stapleton and Weinstein found the rational answer at every prime and heightSource 3. It is an exterior algebra on n generators in degrees −1, −3, −5 and so on. At height 2 this gives one rational copy in each of the degrees 0, −1, −3 and −4. At height 3 there are 8 such copies in total. But as the example shows, this leaves the torsion open.

Hovey and Strickland asked whether each homotopy group is finitely generated over the p-adic integers ℤ_p. Height one was known from a classical calculation. At height two and p at least 5, their analysis of Shimomura's calculations gave the answerSource 4. The paper claims a yes at every prime, every positive height and every degreeSource 5. This answers their questionSource 6. In particular, the torsion part is finite in each degreeSource 7.

The route goes through the Moore spectrum, the version of the sphere with p divided out. Known spectral sequence tools reduce the problem to a finiteness statement about group cohomology. Group cohomology measures how a group acts on a module. If that is finite for the Moore spectrum, the homotopy is finite in each degreeSource 8. Proving that finiteness is the main task of the paperSource 9. It works down through the heights one at a timeSource 10. It uses the geometry of the Fargues–Fontaine curve, an object from p-adic geometry. No uniform bound on the number of generators is claimedSource 11.

How sure is this? There is no Lean check. A computer proof checker has not looked at any part of it. The paper is long and draws on deep tools from p-adic geometry. No specialist review of the paper has been published.

What it doesn't show. This does not give a uniform bound on the number of generators or the torsion size across primes, heights or degrees.

Where it came from

This result comes from an unreleased OpenAI model, published in the openai/math release on 6 October 2026.

Hype check

Major if the proof holds. It is a qualitative finiteness result with no uniform bound. There is no Lean check and no published specialist review.

Words used

K(n)-local sphere: The part of the sphere's stable homotopy theory seen by the Morava K-theory at height n.
Height: The index n of a layer in chromatic homotopy theory.
Finitely generated: Every element can be built from a fixed finite list of elements.
p-adic integers ℤ_p: A number system in which numbers are close when their difference is divisible by a high power of p.
Torsion: Elements that give zero when multiplied by some whole number.
Moore spectrum: The version of the sphere in which multiplication by p is divided out.
Group cohomology: An algebraic measure of how a group acts on a module.

The original paper

Finite generation for the K(n)-local sphere (PDF, opens in a new tab)
September 24, 2026

All quoted lines (11)

These conclusions do not bound the size of integral torsion: the compact module $\prod_{j\geq1}\Fp$ has zero rationalization and exponent $p$ , but is not finitely generated over $\Zp$ .
Finite generation for the K(n)-local sphere Back to text
Even for the sphere, the localized spectrum is not connective, and a degreewise finiteness statement must control each integer degree without a connectivity assumption.
Finite generation for the K(n)-local sphere Back to text
Barthel–Schlank–Stapleton–Weinstein determined the rational answer at every prime and height: $\Q\otimes_{\Z}\pi_*L_{K(n)}S \cong \Lambda_{\Qp}(\zeta_1,\ldots,\zeta_n), \qquad |\zeta_i|=1-2i.$
Finite generation for the K(n)-local sphere Back to text
At height two and $p\geq5$ , Hovey–Strickland's analysis of Shimomura's calculations proves that $\pi_aL_{K(2)}F$ is finite for every finite torsion spectrum $F$ and every integer $a$ .
Finite generation for the K(n)-local sphere Back to text
We prove that the homotopy groups of the $K(n)$ -local sphere are finitely generated $\mathbb Z_p$ -modules in every integer degree, for every prime $p$ and positive height $n$ .
Finite generation for the K(n)-local sphere Back to text
This answers the degreewise finiteness question of Hovey and Hovey–Strickland.
Finite generation for the K(n)-local sphere Back to text
The present theorem proves that the torsion subgroup is finite in each integer homotopy degree.
Finite generation for the K(n)-local sphere Back to text
Consequently, finite coefficient cohomology for the Moore spectrum is enough to obtain finite homotopy in each degree.
Finite generation for the K(n)-local sphere Back to text
Establishing that coefficient finiteness is the main task of this paper.
Finite generation for the K(n)-local sphere Back to text
We prove coefficient finiteness by downward induction from $A_n$ .
Finite generation for the K(n)-local sphere Back to text
There is no uniform bound asserted on the number of generators or on the order of the torsion as $p$ , $n$ , or $t$ varies.
Finite generation for the K(n)-local sphere Back to text

Other sources

openai/math release notes (2026): model provenance and review status manuscripts and supporting proof artifacts produced by an internal OpenAI model

311The Hovey–Strickland and Chai conjecturesTopology
318Chromatic splitting: filtrations and counterexamplesTopology
307Failure of rational injectivity for maximal coarse assemblyTopology
306The purely cosmetic surgery conjectureTopology
312The Grothendieck homotopy hypothesisTopology

Browse Topology Open since the 1990s Claimed, not yet checked

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