OpenAI reports cotype–cotype equivalence under approximation

For a nonzero real Banach space with the ordinary approximation property, K-convexity holds if and only if both the space and its dual have finite Rademacher cotype, with possibly different exponents.

Sources for this record

What was already known

K-convexity was known to imply finite cotype on both sides. Recovering K-convexity from that pair of cotype conditions was the unresolved direction; the manuscript establishes it under the ordinary approximation property.

AI involvement AI-led

OpenAI credits itself as manuscript author and states that its internal frontier model produced the results in this release. Individual human input is not detailed enough to establish task-only autonomy.

OpenAI is named as author on the manuscript, and its release attributes the results to an internal frontier model. The individual human input is not detailed enough to establish autonomy.

Importance Notable

Resolves the cotype–cotype conjecture for the broad class of Banach spaces with the approximation property.

Limitations

The converse direction depends on the approximation property; the paper does not claim the equivalence for all Banach spaces.

Technical verification Formal (Lean 4)

OpenAI reports a Lean proof matching the selected claim.

Formal checking

The pinned Lean note proves the equivalence for every nonzero real Banach space with the ordinary approximation property.

Checker
OpenAI-reported Lean 4 / Comparator
Scope
For a nonzero real Banach space with the ordinary approximation property, K-convexity holds if and only if both the space and its dual have finite Rademacher cotype, with possibly different exponents.
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Few

Few is the default when evidence for a higher level is insufficient. No named person is documented as explaining the central argument for this assessed contribution.

Correction and publication history

2026-10-18 · publication

Primary manuscript, attribution, prior-work, and scoped checking review for non-notifying local inclusion.

Read this published revision