Complex analysis: determine whether a family of functions is a normal family

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SUMMARY

The discussion centers on determining whether the family of analytic functions F, mapping the open unit disc D(0,1) into the region U defined by -2 < u < 2 and satisfying f(0)=0, constitutes a normal family. The key theorem referenced is Montel's theorem, which states that a family of analytic functions that is bounded on compact subsets of a domain contains a uniformly convergent subsequence. The initial approach involves applying the Schwarz lemma to simplify the problem, but the complexity arises from the broader mapping into U, which complicates the bounding conditions necessary for normality.

PREREQUISITES
  • Understanding of analytic functions and their properties
  • Familiarity with the concept of normal families in complex analysis
  • Knowledge of Montel's theorem and its implications
  • Basic grasp of the Schwarz lemma and the maximum modulus principle
NEXT STEPS
  • Study the implications of Montel's theorem in various contexts of complex analysis
  • Explore the Schwarz lemma in detail and its applications to bounded analytic functions
  • Investigate the maximum modulus principle and its role in analyzing families of functions
  • Review examples of normal families and conditions for normality in complex analysis
USEFUL FOR

Students and researchers in complex analysis, particularly those focusing on the properties of analytic functions and normal families, will benefit from this discussion.

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Homework Statement



Let F be the set of all analytic functions f that map the open unit disc D(0,1) into the set U = \left\{w=u+iv : -2 &lt; u &lt; 2 \right\} such that f(0)=0. Determine whether or not F is a normal family.

Homework Equations



DEF&#039;N: A normal family on a domain (i.e. open and connected) U\subset ℂ is a family of analytic functions such that every sequence in the family has a subsequence that converges uniformly on compact subsets of U.

THEOREM(Montel's):
Version 1: A family of analytic functions that is bounded on compact subsets of a domain contains a sequence that converges uniformly on compact subsets (bounded on compact subsets means that for each compact subset there is some positive bound that holds for every function in the family. The constant can depend on the subset but NOT on the function or the point z).

Version 2: If every function in the family is bounded by the same positive constant on the domain then there exists a sequence in the family that converges uniformly on compact subsets.

The Attempt at a Solution



My first thought was to simplify by considering only functions from D \rightarrow D. Schwarz lemma says that since f(0)=0 and |f(z)|\leq 1 then |f(z)| \leq |z|. Hence we can apply the above theorem since we have a bound over the domain and conclude that this "subfamily" is normal. Too bad the real problem isn't this easy! I'm having a tough time figuring this out for the family F. First of all, it only states that the functions are into U. So the mapping can be ANY one-to-one map into ANY subset of U. I've also thought about using maximum modulus principle, but this only gives me bounds on each particular function, rather than the whole family.

Any clues would be greatly appreciated! (EDIT: not even sure if my above statements are entirely correct since I'm pretty confused at this exact moment)
 
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Can i just use compactness and be done? (EDIT no i think that's wrong)
 
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