Theorem: distinct-frequency orthogonality integral_0^{2pi} cos(t) cos(2t) dt = 0

Theorem (Milankovitch spectral-orthogonality canonical): on the fundamental period [0, 2 pi], distinct-frequency cosines are L^2-orthogonal: integral_0^{2 pi} cos(m t) cos(n t) dt = 0 for m != n (Fourier 1822). Each Milankovitch tone…