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Mittag-Leffler: constructing analytic functions with prescribed isolated singular parts

Contribution grade

Complex analysis and meromorphic functions · Exact theorem and reusable mathematical method

Reference score220,000Provisional editorial estimate of this exact contribution; its grade is assessed separately.

What changed

Mittag-Leffler's1884 memoir constructs a single-valued analytic function with prescribed singular parts at a countable isolated setQ, regular away fromQand its accumulation setQprime. Subtracting suitable finite Taylor/rational correction terms from each prescribed part makes their series locally uniformly convergent. Finite polynomial principal parts give the familiar meromorphic-function construction; entire functions of1/(z−a)allow isolated essential singular parts as well. Section 1also treats the stated connected-domain boundary formulation and describes the remaining freedom by addition of a regular function.

Scientific scope

Mittag-Leffler's1884 memoir constructs a single-valued analytic function with prescribed singular parts at a countable isolated setQ, regular away fromQand its accumulation setQprime. Subtracting suitable finite Taylor/rational correction terms from each prescribed part makes their series locally uniformly convergent. Finite polynomial principal parts give the familiar meromorphic-function construction; entire functions of1/(z−a)allow isolated essential singular parts as well. Section 1also treats the stated connected-domain boundary formulation and describes the remaining freedom by addition of a regular function. Accumulation points ofQare excluded; a set merely countable but not isolated is insufficient, and local-uniform convergence is away from the excluded singular set. A finite singular-part polynomial produces a pole, while a transcendental entire function of1/(z−a)generally produces an essential singularity: these cases are not interchangeable. The meromorphic function is not unique without further normalization; on the whole plane two solutions with the same principal parts differ by an entire function. This record covers Section 1, not all 79 pages, later sheaf-cohomological formulations, interpolation with arbitrary zero controls or every general Riemann surface.

Evidence

The linked original works support the scoped statement and contribution attribution. WRS has not independently replayed experiments or reconstructed a full mathematical proof. Accumulation points ofQare excluded; a set merely countable but not isolated is insufficient, and local-uniform convergence is away from the excluded singular set. A finite singular-part polynomial produces a pole, while a transcendental entire function of1/(z−a)generally produces an essential singularity: these cases are not interchangeable. The meromorphic function is not unique without further normalization; on the whole plane two solutions with the same principal parts differ by an entire function. This record covers Section 1, not all 79 pages, later sheaf-cohomological formulations, interpolation with arbitrary zero controls or every general Riemann surface.

Contributors

Provisional WRS assessment, edition 2026-10-23.3. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.

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