In the text by Joseph Bak,(adsbygoogle = window.adsbygoogle || []).push({});

He is trying to determine all automorphisms of the unit disk such that f(a)=0.

He says "let us suppose that this automorphism is a linear fractional transformation. Then it must map the unit circle onto the unit circle.

I am asking for help in understanding this deduction/conclusion.

Thank you

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# Complex analysis/linear fractional transformation

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