Weak pure infiniteness and Cuntz-algebra absorption. Resolves the ordinary-to-strong pure-infiniteness question of Kirchberg and Rørdam for complex C∗-algebras. For exact algebras, proper infiniteness of one fixed finite amplification of every positive element also suffices. Consequently, every separable nuclear algebra with this property absorbs $\mathcal O_\infty$, without unitality or simplicity assumptions.
released 2026-09-25 | 3 theorems · 22 lemmas · 38 proofs · 22,306 words |
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We prove that every complex C∗-algebra in which each positive element is properly infinite is strongly purely infinite. This answers the ordinary-to-strong part of Kirchberg–Rørdam's comparison question. For exact algebras, we also prove that proper infiniteness of one fixed finite amplification of every positive element implies proper infiniteness of each positive element. Consequently, every separable nuclear algebra with this fixed-amplification property absorbs $\mathcal O_\infty$, without assumptions of unitality or simplicity.