Solution

ID: past-exam-of-the-algebra-analysis-and-differential-equations-2-course-of-the-university-of-oxford/2012/4/c/ii/solution

Either equality condition says that the holomorphic function from part (i) has modulus one at an interior point: at zero in the derivative case, or at the given nonzero point in the other case. Since everywhere, the maximum modulus principle makes a constant with . Therefore
These maps are rotations of the unit disk and do achieve both equalities, so this also identifies all equality cases of the Schwarz lemma.

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