Nonlinearity is surely an old and hard problem, as history shows. Topological physics may provide a new viewpoint for it. The paper “Topological-to-topological transition induced by on-site nonlinearity in a one-dimensional topological insulator” by Kazuki Sone and Yasuhiro Hatsugai has been accepted for publication in Physical Review Research on 19 December, 2025. Have a look at. See also arXiv:2501.10087.