2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/184024We discuss the problem of the small ratio of muon mass to tau mass in a class of seesaw models where maximal atmospheric neutrino mixing is enforced through a $μ$--$τ$ interchange symmetry. We introduce into those models an additional symmetry $T$ such that $m_μ= 0$ in the case of exact $T$ invariance. The symmetry $T$ may be softly broken in the Higgs potential, and one thus achieves $m_μ\ll m_τ$ in a technically natural way. We speculate on a wider applicability of this mechanism.10 pages, plain LaTeX, no figures, minor changes, final version for J. Phys. GHigh Energy Physics - Phenomenologytext