analysis / Operator algebras; C*-algebras, pure infiniteness

Kirchberg-Rordam comparison question: pure infiniteness implies strong pure infiniteness, and weak equals strong for exact C*-algebras

Theorem 1.1: every complex C*-algebra in which every positive element is properly infinite is strongly purely infinite, with an arbitrary cross term in the diagonalization. Theorem 1.2: for exact algebras, proper infiniteness of h⊕nh^{\oplus n} for one fixed nn and all positive hh implies proper infiniteness of every positive element, hence strong pure infiniteness. Corollary: a separable nuclear algebra with this fixed-amplification property absorbs O∞\mathcal O_\infty, with no unitality or simplicity assumption (via Kirchberg's central-sequence results). Not settled: whether weak pure infiniteness implies pure infiniteness for non-exact algebras, which the paper states remains outside its conclusions.

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analysisSep 25, 2026Significance 27/100Registry: lean checked

Kirchberg-Rordam comparison question: pure infiniteness implies strong pure infiniteness, and weak equals strong for exact C*-algebras

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Theorem 1.1: every complex C*-algebra in which every positive element is properly infinite is strongly purely infinite, with an arbitrary cross term in the diagonalization. Theorem 1.2: for exact algebras, proper infiniteness of h⊕nh^{\oplus n} for one fixed nn and all positive hh implies proper infiniteness of every positive element, hence strong pure infiniteness. Corollary: a separable nuclear algebra with this…

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Theorem 1.1: every complex C*-algebra in which every positive element is properly infinite is strongly purely infinite, with an arbitrary cross term in the diagonalization. Theorem 1.2: for exact algebras, proper infiniteness of h⊕nh^{\oplus n} for one fixed nn and all positive hh implies proper infiniteness of every positive element, hence strong pure infiniteness. Corollary: a separable nuclear algebra with this fixed-amplification property absorbs O∞\mathcal O_\infty, with no unitality or simplicity assumption (via Kirchberg's central-sequence results). Not settled: whether weak pure infiniteness implies pure infiniteness for non-exact algebras, which the paper states remains outside its conclusions.

Theorem 1.1: every complex C*-algebra in which every positive element is properly infinite is strongly purely infinite, with an arbitrary cross term in the diagonalization. Theorem 1.2: for exact algebras, proper infiniteness of h⊕nh^{\oplus n} for one fixed nn and all positive hh implies proper infiniteness of every positive element, hence strong pure infiniteness. Corollary: a separable nuclear algebra with this fixed-amplification property absorbs O∞\mathcal O_\infty, with no unitality or simplicity assumption (via Kirchberg's central-sequence results). Not settled: whether weak pure infiniteness implies pure infiniteness for non-exact algebras, which the paper states remains outside its conclusions.

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