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A counterexample to the hyperinvariant-subspace problem
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Skills:infinite matrices Levels:2
Category:Operator algebras Lean version:YES! ✔
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Invariant projections, hyperinvariant subspaces, and transitive algebras. Constructs a nonzero norm-quasinilpotent operator on every infinite-dimensional separable complex Hilbert space with no nonzero proper closed subspace invariant under every commuting operator. The construction also gives operators with no nontrivial invariant projection in the hyperfinite type II1 factor.

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released 2026-09-27  |  3 theorems · 18 lemmas · 27 proofs · 19,345 words  |  PLAY LEVEL 1 »  (pdf)
For every irrational angle, we construct a continuous nonnegative circle weight with exactly one zero and logarithmic integral $-\infty$ whose weighted rotation has no nontrivial invariant projection in the associated hyperfinite type II1 factor. This answers negatively the question of Zhu, Fang, and Shi, with the angle prescribed in advance. The resulting operator is nonzero and norm-quasinilpotent.
released 2026-09-27  |  1 theorem · 5 lemmas · 9 proofs · 5,766 words  |  PLAY LEVEL 2 »  (pdf)
We give a negative answer to the hyperinvariant-subspace problem by constructing, on every infinite-dimensional separable complex Hilbert space, a nonzero bounded norm-quasinilpotent operator with no nonzero proper closed hyperinvariant subspace. Its commutant is a proper strongly closed unital transitive complex operator algebra.

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