ICC property (T) groups without W*-superrigidity

Shuoxing Zhou

Zhou constructs two nonisomorphic countable ICC property-(T) groups whose group von Neumann algebras are isomorphic. A quadratic fiber shear identifies the dual actions, while the groups have distinct module structures.

Sources for this record

What was already known

Connes’ W*-superrigidity conjecture predicted this could not happen. An independent concurrent OpenAI binary-carry construction also refutes it and yields an infinite family.

AI involvement AI-led

Zhou credits GPT-5.6 Sol, Codex and Danus with finding the main construction under his mathematical guidance. He reorganized, revised and checked the material and explains the mechanism.

The AI-use statement credits the principal construction mainly to three AI systems under Zhou's guidance.

Importance Notable

Adds an explicit counterexample with a different fixed-group and action mechanism; priority for the disproof is shared or unsettled.

Limitations

Lean checked selected unspecified parts. Zhou reports checking the revised material, but the source does not identify a completed check of every theorem clause.

Technical verification Partial

Lean 4.32.1 checked selected, unspecified parts, and Zhou reports checking the revised material. Neither account identifies a completed rigorous review of all four theorem clauses and their interface, so the full counterexample is not rated Formal.

Human understanding Full

Zhou mathematically guided and revised the construction and presents its central mechanism: dual-action conjugacy by a quadratic shear versus distinct module structures. This explains the assessed construction, although it does not certify every proof step.

Correction and publication history

2026-10-18 · publication

Adds an explicit counterexample with a different fixed-group and action mechanism; priority for the disproof is shared or unsettled.

Read this published revision