Let and consider the integral , where is the rectangular contour with vertices at and (for some large real number R). The only singularity of the integrand is at 0 (and hence not inside the contour) so the integral is zero. The components of the integral along the top and bottom segments of the contour will be small for large R, so the integrals along the vertical segments will be similar, and in fact will coincide in the limit as R→∞. Hence .