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1 Introduction
Representations of A in which τ is unitarily implemented in the sense of the first relation of (1.4.7) are called τ −covariant representations. In such representations, the
action of τ is given by an ‘observable’—the selfadjoint generator of the corresponding unitary group acting on the Hilbert space of the representation. An interpretation
of such a generator might be dependent, however, on the choice of the covariant
representation.