Fourier representation of a Kronecker delta
= Fourier representation of a Kronecker delta
{c}
{title2=$\delta_{nm}=(2\pi)^{-1}\int_0^{2\pi}e^{i(n-m)\theta}\,d\theta$}
Orthogonality of integer-frequency <Fourier modes> gives this identity: the integral is one for $n=m$ and zero otherwise. It converts integer step-count constraints into products of generating functions, as in the <dilute-hopping lattice propagator>.