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COMPLEX ANALYSIS / INTRODUCTORY EXPOSITION

Cauchy integral formula.

Holomorphic functions and contour integrals

Editorially prepared introduction for this redesigned journal. This is new explanatory content, separate from Pablo's original notes.

1. Holomorphic functions

A complex function is holomorphic if it is complex differentiable on an open set. Holomorphicity has much stronger consequences than ordinary real differentiability.

2. Cauchy's integral formula

Theorem. If \(f\) is holomorphic on an open neighborhood of a closed disk, and \(\gamma\) positively traverses its boundary, then for any interior point \(a\), \[f(a)=\frac{1}{2\pi i}\oint_\gamma\frac{f(z)}{z-a}\,dz.\]

3. Higher derivatives

Differentiating the integral formula yields \[f^{(n)}(a)=\frac{n!}{2\pi i}\oint_\gamma\frac{f(z)}{(z-a)^{n+1}}\,dz.\]

Consequence. A holomorphic function is infinitely complex differentiable and locally admits a convergent Taylor series.

4. Zeros, poles, and meromorphic functions

Meromorphic functions are holomorphic except at isolated poles. Their zeros and poles carry algebraic information—an idea developed further in the existing Undergraduate Seminar V paper.

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