2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/26935Recent inelastic-neutron-scattering measurements of a low-energy phonon in Bi_2Sr_2CaCu_2O_8 provide enough information to place a lower bound on the energy gap magnitude at precise locations on the Fermi surface. Measurements of a few low-energy phonons should indicate whether the gap symmetry is d_{x^2-y^2}. Further measurements could map out the angle-resolved gap magnitude on the entire Fermi surface.7 pages + 1 figure (included), plain tex, NSF-ITP-93-16Condensed Mattertext