. Suppose f is C-analytic in D(0; 1) and maps the unit circle into itself. Show then that f maps the entire disc onto itself. [Hint: Use the Maximum-Modulus Theorem to show that f maps D(0; 1) into itself. Then apply the previous exercise to conclude that the mapping is onto.]

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4. Suppose f is C-analytic in D(0; 1) and maps the unit circle into itself. Show then that f maps the
entire disc onto itself. [Hint: Use the Maximum-Modulus Theorem to show that f maps D(0; 1) into
itself. Then apply the previous exercise to conclude that the mapping is onto.]
Transcribed Image Text:4. Suppose f is C-analytic in D(0; 1) and maps the unit circle into itself. Show then that f maps the entire disc onto itself. [Hint: Use the Maximum-Modulus Theorem to show that f maps D(0; 1) into itself. Then apply the previous exercise to conclude that the mapping is onto.]
het D denote D(0,1) and cl (D) the closed disc {12/51}
The maximum modulus theorem gives that
f maps D into itself. So the issue is showing that
it is onto
Proof:
By the open mapping theorem PCD) is open,
So f (D)n D is open. Since cl CD) is Compact,
f (c (D)) is also compact.
Hence f(cl(D)) D is a relatively closed subset of D.
gimce f takes {121=1} to {121=1},
f (c (D)) DD= f(D) AD.
Hence f(D) AD is open, closed and nonempty
Subset of D. Hence by connection connectedness of D
you have that f(D) AD = D which means f is onto
as well.
Transcribed Image Text:het D denote D(0,1) and cl (D) the closed disc {12/51} The maximum modulus theorem gives that f maps D into itself. So the issue is showing that it is onto Proof: By the open mapping theorem PCD) is open, So f (D)n D is open. Since cl CD) is Compact, f (c (D)) is also compact. Hence f(cl(D)) D is a relatively closed subset of D. gimce f takes {121=1} to {121=1}, f (c (D)) DD= f(D) AD. Hence f(D) AD is open, closed and nonempty Subset of D. Hence by connection connectedness of D you have that f(D) AD = D which means f is onto as well.
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