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3. ... or may not be observable. For a selection of the literature, see J.A. Wheeler and W.H. Zurek, eds.,Quantum Theory and Measurement (Princeton University Press, Princeton, 1983).
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5. We comment on the extent to which our conclusions depend on the harmonic oscillator form of the potential. IfV is nonsingular andV(x) ? ? for |x| ? ?, it is clear that there exists $$\bar W$$ (x 1,x 2), independent ofT, such that min ? W(?;x 1, 0,x 2,T) ? $$\bar W$$ (x 1,x 2). Moreover, even ifV(x) ? 0 for |x| ? ?, so long asV has bound states the minimum value ofW does not grow indefinitely withT. The peculiarity of the harmonic oscillator is that it can periodically achieve perfect focussing.