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Article Contents

ABSTRACT

1.CONTEXT

2.H₀ FROM TIME DELAYS CIRCA 2003

3.LENSING FUNDAMENTALS

3.1.The 3 D's

3.2.Modeling the lens

4.PROBLEM LENSES

4.1.Kochanek's time delay formulation

4.2.The mass sheet degeneracy

4.3.The central concentration degeneracy

4.4.Multiple lenses

4.5.Microlensing

4.6.The myth of quasar variability

5.A GOLDEN LENS

6.SUMMARY AND PROSPECTS

REFERENCES