analysis / Operator algebras

The generator problem: is every von Neumann algebra with separable predual singly generated?

Theorem 1.2: every type II1\mathrm{II}_1 factor with separable predual is W∗(x)W^*(x) for one xx (two self-adjoint generators). Theorem 1.1: for an irreducible inclusion P⊂MP\subset M of II1\mathrm{II}_1 factors, MM separable, the unitaries uu with W∗(P,u)=MW^*(P,u)=M are a dense GδG_\delta in the 2-norm topology. With Willig's reduction this gives single generation of every von Neumann algebra with separable predual. Consequences: the generator invariants GG and GsaG_{sa} vanish, and Voiculescu's δ,δ0\delta,\delta_0 are not W∗W^*-invariants on L(Fn)L(\mathbb F_n), n≥3n\ge3. No explicit generator is constructed.

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analysisSep 23, 2026Significance 50/100Registry: lean checked

The generator problem: is every von Neumann algebra with separable predual singly generated?

Prior state unknown→proved

Theorem 1.2: every type II1\mathrm{II}_1 factor with separable predual is W∗(x)W^*(x) for one xx (two self-adjoint generators). Theorem 1.1: for an irreducible inclusion P⊂MP\subset M of II1\mathrm{II}_1 factors, MM separable, the unitaries uu with W∗(P,u)=MW^*(P,u)=M are a dense GδG_\delta in the 2-norm topology. With Willig's reduction this gives single generation of every von Neumann algebra with separable predual. Consequ…

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Theorem 1.2: every type II1\mathrm{II}_1 factor with separable predual is W∗(x)W^*(x) for one xx (two self-adjoint generators). Theorem 1.1: for an irreducible inclusion P⊂MP\subset M of II1\mathrm{II}_1 factors, MM separable, the unitaries uu with W∗(P,u)=MW^*(P,u)=M are a dense GδG_\delta in the 2-norm topology. With Willig's reduction this gives single generation of every von Neumann algebra with separable predual. Consequences: the generator invariants GG and GsaG_{sa} vanish, and Voiculescu's δ,δ0\delta,\delta_0 are not W∗W^*-invariants on L(Fn)L(\mathbb F_n), n≥3n\ge3. No explicit generator is constructed.

Theorem 1.2: every type II1\mathrm{II}_1 factor with separable predual is W∗(x)W^*(x) for one xx (two self-adjoint generators). Theorem 1.1: for an irreducible inclusion P⊂MP\subset M of II1\mathrm{II}_1 factors, MM separable, the unitaries uu with W∗(P,u)=MW^*(P,u)=M are a dense GδG_\delta in the 2-norm topology. With Willig's reduction this gives single generation of every von Neumann algebra with separable predual. Consequences: the generator invariants GG and GsaG_{sa} vanish, and Voiculescu's δ,δ0\delta,\delta_0 are not W∗W^*-invariants on L(Fn)L(\mathbb F_n), n≥3n\ge3. No explicit generator is constructed.

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