OpenAI reports a reflexive midpoint-convexity counterexample

A separable reflexive real Banach space has an asymptotically midpoint uniformly convex given norm with averaged midpoint modulus at least √(1+t²/12)−1 for t>0, but admits no equivalent asymptotically uniformly convex norm; depth-k countably branching diamonds have distortion at least √(1+k/12) in it.

Sources for this record

What was already known

The general midpoint-convexity versus asymptotic-uniform-convexifiability question had already been answered negatively by Baudier. The manuscript supplies a reflexive example with an explicit modulus and answers a separate reflexive diamond-distortion question.

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

Strengthens the earlier negative result to a quantitative reflexive example and separates the corresponding metric diamond criterion.

Limitations

This is not the first negative answer to the general renormability question. The numerical bounds refer to the constructed norm and countably branching diamonds.

Technical verification Formal (Lean 4)

OpenAI reports a Lean proof matching the selected claim.

Formal checking

The pinned Lean note proves reflexivity, the averaged midpoint modulus, failure of every equivalent AUC norm and the diamond-distortion lower bound.

Checker
OpenAI-reported Lean 4 / Comparator
Scope
A separable reflexive real Banach space has an asymptotically midpoint uniformly convex given norm with averaged midpoint modulus at least √(1+t²/12)−1 for t>0, but admits no equivalent asymptotically uniformly convex norm; depth-k countably branching diamonds have distortion at least √(1+k/12) in it.
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