OpenAI reports a counterexample to Kaplansky’s quasitrace conjecture

There is a separable unital complex C∗-algebra with normalized 2-quasitraces but no tracial state; its quasitraces fail additivity on a fixed pair of positive contractions.

Sources for this record

What was already known

Kaplansky’s quasitrace conjecture predicted that every 2-quasitrace on a C∗-algebra is additive and hence a trace; the general question was unresolved.

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 Major

Refutes Kaplansky’s quasitrace conjecture and overturns a proposed general identification of quasitraces with traces.

Limitations

This selected contribution is the quasitrace counterexample. The same Lean note separately records tensor-product failures of stable finiteness.

Technical verification Formal (Lean 4)

OpenAI reports a Lean proof matching the selected claim.

Formal checking

The pinned Lean note constructs the algebra and fixed positive contractions, with a quantified failure of additivity for every normalized 2-quasitrace.

Checker
OpenAI-reported Lean 4 / Comparator
Scope
There is a separable unital complex C∗-algebra with normalized 2-quasitraces but no tracial state; its quasitraces fail additivity on a fixed pair of positive contractions.
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