2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/2244A procedure is suggested for systematically narrowing the choice of possible primaries for (UHECR) air showers with energies beyond the Greisen-Zatsepin-Kuz'min cut-off of $4 \times 10^{19} eV$.13 pages, Latex, 2 figures using epsAstrophysicsHigh Energy Physics - Phenomenologytext