Author

Alexandru Chirvăsitu

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Preprint Sep 2026

Weak$^*$ polynomial density, diffuseness and proper infinitude

The unitary group of a von Neumann algebra on an $\aleph_0$-dimensional Hilbert space is polynomially weak$^*$-dense (equivalently, $G_{delta}$ dense or residual) in the normal unit ball if and only if the canonical finite atomic quotient of the von Neumann algebra is trivial. The analogous result holds for the usual w...

Alexandru Chirvăsitu · 0 citations

Preprint Aug 2026

Ergodic-transformation centralizers and essentially non-compact graphing symmetry

We prove that for every ergodic transformation $T$ on an infinite standard probability space both the automorphism group (i.e. centralizer) $\mathrm{Aut}(T)$ and its reversing automorphism group are realizable as symmetry groups of graphings. This is an analogue of Sabidussi's realization of arbitrary graph-automorphis...

Alexandru Chirvăsitu · 0 citations