Abstract
1. Introduction. One of the striking results of the work done by Murray and von Neumann (9) in the analysis of rings of operators on a Hilbert space is the reduction of the unitary equivalence problem for certain types of factors to the problem of algebraic equivalence. Roughly speaking, they associate with each concrete representation of a factor a number (which measures the relative size of the factor and its commutant)—the so-called “coupling constant.”

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