2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/93252If scattering amplitudes are ordinary complex numbers (not quaternions) there is a universal algebraic relationship between the six coherent cross sections of any three scatterers (taken singly and pairwise). A violation of this relationship would indicate either that scattering amplitudes are quaternions, or that the superposition principle fails. Some possible experimental tests involve neutron interferometry, K_S-meson regeneration, and low energy proton-proton scattering.7 pages LaTeX, to appear in "Quantum Interferometry" VCH Publishers (1996), edited by F. De MartiniQuantum Physicstext