2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/125936It is shown that among all tight designs in FP^n, where F is R, C, or H (quaternions), other than RP^1, only 5-designs in CP^1 have irrational angle set. This is the only case of equal ranks of the first and the last irreducible idempotent in the corresponding Bose-Mesner algebra.10 pages, no figuresCombinatorics05B30text