Residue is a complex number proportional to a contour integral over a path around a pole a of a meromorphic function f. It is denoted as . The value of the residue of a pole is given by In the case of a simple pole (a pole with a multiplicity of 1) this formula reduces to If f(z) can be expressed as the quotient of two holomorphic functions, and h'(c) ≠0, this formula further reduces to By Cauchy's integral formula, residue is related to the contour integral by