2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69255We show that every trivial 3-strand braid diagram contains a disk, defined as a ribbon ending in opposed crossings. Under a convenient algebraic form, the result extends to every Artin--Tits group of dihedral type, but it fails to extend to braids with 4 strands and more. The proof uses a partition of the Cayley graph and a continuity argument.Geometric Topology57M25, 20F36text