Solution
= Solution
The coefficient of $z^{-1}$ in the <Laurent series> is $-1$. The <residue theorem> therefore gives, for the standard positive orientation,
$$
\boxed{\oint_Ce^{-1/z}\,dz=2\pi i\operatorname{Res}_{z=0}e^{-1/z}=-2\pi i.}
$$
The <residue theorem> applies to an isolated <essential singularity> as well as to a <pole>.