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A meromorphic essential singularity omits at most two sphere values
Statement
Let be meromorphic on a punctured disc with an essential singularity at . Then at most two sphere values can be omitted on a punctured neighborhood of ; equivalently, with at most two sphere-value exceptions, every value occurs infinitely often in every punctured neighborhood of .
Facts & Assumptions
Given: A meromorphic function with an essential singularity on .
Great Picard holds for holomorphic functions and finite values (Great Picard theorem).
Möbius transformations act biholomorphically on the sphere and can move any ordered triple of sphere points to any other (Every Möbius transformation is a biholomorphism of the Riemann sphere, A unique Möbius transformation carries any ordered triple of distinct sphere points to any other).
Proof
Suppose three distinct sphere values each failed to occur infinitely often in some punctured neighborhood of . After passing to a common smaller neighborhood and then shrinking past their finitely many preimages, all three values are omitted. By [L2], choose a Möbius transformation sending them to , , and . Then is holomorphic on that smaller punctured disc and still has an essential singularity at , because a biholomorphic target change cannot turn an essential singularity into a removable singularity or pole.
The function omits the finite values and , so [L1] gives a contradiction. Thus at most two sphere values can fail the infinitely-often property, and every other sphere value occurs infinitely often in every punctured neighborhood.
This is the meromorphic Great Picard conclusion.
Depends on
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
8 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Aleksander Simonic, The Ahlfors lemma and Picard's theorems (standard reference, not scraped)