### Abstract

In complex analysis, the winding number measures the number of times a
path (counterclockwise) winds around a point, while the Cauchy index
can approximate how the path winds. This entry provides a
formalisation of the Cauchy index, which is then shown to be related
to the winding number. In addition, this entry also offers a tactic
that enables users to evaluate the winding number by calculating
Cauchy indices.