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Published online by Cambridge University Press: 25 May 2016
The statistics of gravitationally lensed quasars requires that λ < 0.7 at 90% confidence. This limit is weakly affected by the evolution of galaxies through merging. If E/S0 galaxies have much higher dust opacities at redshifts of 0.5-1.0 than they do locally, these limits can be evaded.