Talk, Mathematics REU, University of Chicago, Chicago, IL, USA
I introduced the group actions on trees, and discussed which groups must act with a fixed point on every tree. A central example is \(\mathrm{SL}_2(\mathbb{Z})\), which can act on a tree without fixed points, while \(\mathrm{SL}_3(\mathbb{Z})\) always fixes a point. Notes
Seminar, School of Mathematical Sciences, Peking University, Beijing, China
This is the “3+X” seminar on CAT(0) Cube Complexes, organized by Prof. Yi Liu, Prof. Jiajun Wang, and Prof. Wenyuan Yang in 2026 Spring at Peking University. The reference is mainly P. Schwer’s CAT(0) Cube Complexes: An Introduction.
Seminar, School of Mathematical Sciences, Peking University, Beijing, China
This is the “3+X” seminar on Knots and Links, organized by Prof. Yi Liu and Prof. Jiajun Wang in 2025 Fall at Peking University. The reference is D. Rolfsen’s Knots and Links.
Seminar, School of Mathematical Sciences, Peking University, Beijing, China
This is the “3+X” seminar on CAT(0) spaces, organized by Prof. Wenyuan Yang in 2025 Fall at Peking University. The reference is M. R. Bridson and A. Haefliger’s Metric Spaces of Non-Positive Curvature.
Seminar, School of Mathematical Sciences, Peking University, Beijing, China
This is the geometry seminar organized by Ziqiang Bao in 2025 Spring at Peking University. The reference is J. Stillwell’s Geometry of Surfaces.
Seminar, School of Mathematical Sciences, Peking University, Beijing, China
This is the “3+X” seminar on Heegaard Splitting, organized by Prof. Yi Liu and Prof. Jiajun Wang in 2025 Spring at Peking University. The reference is M. Scharlemann’s Heegaard splittings of compact 3-manifolds.