2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/222397Let K be a knot that has an unknotting tunnel tau. We prove that K admits a strong involution that fixes tau pointwise if and only if K is a two-bridge knot and tau its upper or lower tunnel.9 pages, 3 figuresGeometric Topology57M25; 57N10text