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Morera's theorem fails without continuity
Statement refuted
Refuted claim: A function on an open subset of whose integral around every contained triangle is zero must be holomorphic, even when continuity is not assumed.
In the edgewise Riemann sense, the function
has zero integral around every complex triangle, but is not holomorphic.
Facts & Assumptions
Given: The displayed function and an arbitrary ordered complex triangle.
If the velocity-weighted pullback of a function along each affine triangle edge is Riemann integrable, its edgewise triangle integral is the sum of those edge integrals (The edgewise Riemann integral around a complex triangle for an integrable pullback).
Changing a real Riemann-integrable function at finitely many points preserves integrability and its integral (Changing an integrable function at finitely many points changes neither its integrability nor its integral).
Every complex differentiable function is continuous at the point of differentiability (Complex differentiability at a point implies continuity there).
Morera's theorem assumes continuity in addition to zero integrals around every contained filled triangle (Morera's theorem: vanishing triangle integrals characterize holomorphy among continuous functions).
Counterexample
Fix an arbitrary triangle and read its boundary integral in the edgewise sense of [L1] for the point-supported function .
The function is discontinuous at , since every punctured neighbourhood contains points where its value is while ; by [L3], it is not complex differentiable, and hence not holomorphic, at .
On a nonconstant affine edge, the edge map is injective and therefore meets at most once, so each real component of its velocity-weighted pullback differs from zero at at most one parameter and [L2] makes its integral zero; on a constant edge the velocity is zero, so its pullback integral is also zero. Hence [L1] gives zero around every triangle, including repeated or collinear vertices.
Steps 2.1 and 1.2 exhibit vanishing edgewise triangle integrals without holomorphy, so removing the continuity hypothesis from [L4] makes the implication false.
Depends on
- Morera's theorem: vanishing triangle integrals characterize holomorphy among continuous functions
- The edgewise Riemann integral around a complex triangle for an integrable pullback
- Changing an integrable function at finitely many points changes neither its integrability nor its integral
- Complex differentiability at a point implies continuity there
Used by
Nothing in the library uses this result yet.
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Sources
- B. V. Shabat, Introduction to Complex Analysis, Remark 2.22 (standard reference, not scraped)