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The Mackey-Gleason Problem

L. J. Bunce·J. D. Maitland Wright
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Abstract

Let $A$ be a von Neumann algebra with no direct summand of Type $\roman I_2$, and let $\scr P(A)$ be its lattice of projections. Let $X$ be a Banach space. Let $m\:\scr P(A)\to X$ be a bounded function such that $m(p+q)=m(p)+m(q)$ whenever $p$ and $q$ are orthogonal projections. The main theorem states that $m$ has a unique extension to a bounded linear operator from $A$ to $X$. In particular, each bounded complex-valued finitely additive quantum measure on $\scr P(A)$ has a unique extension to a bounded linear functional on $A$.

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L. J. Bunce, J. D. Maitland Wright. 1992-04-01. The Mackey-Gleason Problem. https://arxiv.org/abs/math/9204228

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