Around the Andreadakis-Johnson filtration
arXiv:2608.26934
Abstract
The Andreadakis-Johnson filtration and its associated construction, known as the Johnson homomorphism, are useful tools in group theory. They provide a step-by-step approach to studying the automorphisms of a given group. After explaining the basics we survey both classical and recent results around the Andreadakis-Johnson filtration, with emphasis on the mapping class group of a once-bordered surface.
18 pages; survey chapter for the book "Nisyros 2025: Essays in Geometry, History and Philosophy", ed. A. Papadopoulos and S. Yamada