In mathematics, a Hankel contour is a path in the complex plane which extends from
[∞,δ], around the origin counter clockwise and back to
[∞,-δ], remaining arbitrarily close to the real axis but without
crossing the real axis except for negative values of x.
Use of Hankel contours is one of the methods of contour integration. This type of path for contour integrals was first used by Hermann Hankel in his investigations of the Gamma function.
The mirror image extending from -∞, circling the origin clockwise, and returning
to -∞ is also called a Hankel contour.