2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/184048With the recent experimental advance in our precise knowledge of the neutrino oscillation parameters, the correct form of the 3 X 3 neutrino mass matrix is now approximately known. I discuss how this may be obtained from symmetry principles, using as examples the finite groups A_4 and Z_3, in two complete theories of leptons (and quarks).15 pages, no figure, talk at 9th Adriatic Meeting, Dubrovnik (September 2003)High Energy Physics - Phenomenologytext