Analyticity and Integrality
Analyticity and the Complex Logarithm We consider a complex-valued function $f$ of one complex variable $z$, and we write: \[ \int_{\mathrm{A}} f(z) d z=(\mathrm{A}, f(z) d z)\] interpreting it as being bilinear in the differential \( f(z) d z \) and the homological $1$-chain \( \mathrm {A} \). Then, if \( f \) is a continuous function of the complex variable \( z \) in the region $\mathbf R$ and if it holds: \[\int_{\mathrm{C}} f(z) d z=0\] about any closed chain $\mathrm {C}$ in \( \mathbf{R}, \) then \( f(z) \) represents an analytic function in $\mathbf {R}$. In practice, if \( f \) is analytic merely on a closed path \( \mathcal{C}, \) it does not follow that \( \int_{\mathrm{C}} f(z) d z=0 . \) In particular, \[\int_{\mathrm{C}} \frac{d z}{z}=2 \pi i\] where \( \mathcal{C} \) is a simple closed curve embracing the origin. This leads to the conclusion that it is precisely the complex logarithm function that characterizes the geometry of the complex plane in all its essential aspe...