# closed curve theorem

Let $U\subset\mathbb{C}$ be a simply connected domain, and suppose $f:U\longrightarrow\mathbb{C}$ is holomorphic. Then

 $\int_{C}f(z)\ dz=0$

for any smooth closed curve $C$ in $U$.

More generally, if $U$ is any domain, and $C_{1}$ and $C_{2}$ are two homotopic smooth closed curves in $U$, then

 $\int_{C_{1}}f(z)\ dz=\int_{C_{2}}f(z)\ dz.$

for any holomorphic function $f:U\longrightarrow\mathbb{C}$.

Title closed curve theorem ClosedCurveTheorem 2013-03-22 12:04:43 2013-03-22 12:04:43 djao (24) djao (24) 7 djao (24) Theorem msc 30E20 CauchyIntegralTheorem