Backward intertwiners and a transitive commutant

OpenAI

On every separable infinite-dimensional complex Hilbert space, the paper constructs a nonzero bounded norm-quasinilpotent operator S whose commutant has no nonzero proper closed invariant subspace. The operator S itself has ordinary invariant subspaces.

Sources for this record

What was already known

The general hyperinvariant-subspace question remained open; earlier weighted-shift results and Arveson’s density theorem had additional hypotheses.

AI involvement AI-led

OpenAI is the credited author and attributes its manuscript and proof artifacts to an internal model. Item-specific autonomy is not documented.

The original manuscript credits OpenAI as author, and the repository explicitly attributes manuscript and proof-artifact production to an internal OpenAI model; result-specific autonomy is not documented.

Importance Major

Negatively answers the hyperinvariant-subspace question in the stated Hilbert-space setting.

Limitations

OpenAI reports Lean checking of the stated operator and commutant properties. No named human whole-proof check or explanation of the construction is documented.

Technical verification Formal (Lean 4 with Comparator)

OpenAI reports a Lean formalization of the unrestricted separable infinite-dimensional complex Hilbert-space existence claim. The comparator challenge states nonzero, quasinilpotent S with a transitive, proper, strongly closed commutant. The public challenge has a sorry placeholder, while the configured solution module is the claimed proof.

Formal checking

Existence, on every separable infinite-dimensional complex Hilbert space, of a nonzero quasinilpotent operator with a proper strongly closed transitive commutant; Source-reported formal proof in OAI.Analysis.Hyperinvariant.Main compared with HyperinvariantSubspaces.lean; permitted axioms propext, Quot.sound and Classical.choice

Checker
Lean 4 kernel and OpenAI Comparator configuration
Scope
Existence, on every separable infinite-dimensional complex Hilbert space, of a nonzero quasinilpotent operator with a proper strongly closed transitive commutant
Basis
Reported by the linked checker
Evidence source

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

Human understanding Few

No identified person's explanation of the model-origin weighted-fiber and backward-intertwiner construction was found; Few is the documentation default, not a report of confusion.

Correction and publication history

2026-10-18 · publication

Negatively answers the hyperinvariant-subspace question in the stated Hilbert-space setting.

Read this published revision