Solution

ID: past-exam-of-the-metric-spaces-and-complex-analysis-course-of-the-university-of-oxford/2014/2/c/solution

Take and the constant contraction mapping . For , ,
No Lipschitz constant less than one can work, so need not be a contraction. More generally, differing only in the second input coordinate already prevents a strict contraction whenever has two points.
If has contraction constant , two iterations give
and consequently
Thus is a contraction mapping. The swap lift of a contraction shows why an iterate can contract even when one step does not.

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