We 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. © 2003 Elsevier Ltd. All rights reserved.
Dehornoy, P. (2004). Disks in trivial braid diagrams. Topology, 43(5), 1067–1079. https://doi.org/10.1016/j.top.2003.11.005