Sang-hyun Kim

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Welcome to Sam Sang-hyun Kim's page

New preprint

We prove that for each real numbers a ≥ 2, there exists a finitely generated subgroup Ga of Diffa(S1) with the property that Ga admits no injective homomorphisms into Diffb(S1) for all b > a. For a > 2, there exists another fg group Ha that embeds into Diffb(S1) for all b < a, but not into Diffa(S1). One can further require the same properties are inherited for all finite index subgroups and for the commutator groups of Ga and of Ha. The commutator groups will be simple.


  • I am on sabbatical for the year of 2017 (March - December).
  • Nov 27 - Dec 20. Japan, China.

Conference organization

  • GAGTA-2018, Organizing/Scientific Committee, Seoul, Korea, Jul 16 - 20, 2018
  • Groups, Geometry and Dynamical Systems (ICM Satellite), Scientific Committee, Montevideo, Uruguay, July 23 - 27, 2018



Sang-hyun Kim, Associate Professor
Department of Mathematical Sciences, Seoul National University
1 Gwanak-ro, Gwanak-gu, Post Code 08826, Seoul, Korea



Office Hour I am on sabbatical. Email me.


CV (2017, PDF)



Geometric group theory: right-angled Artin group, hyperbolic group, mapping class group, diffeomorphism group, acute triangulations.

Publications & Talks

  • Selected publications
15. (With Cheol-Hyun Cho, Hansol Hong and Siu-Cheong Lau), Lagrangian Floer potential of orbifold spheres, Advances in Mathematics Volume 306, 14 January 2017, Pages 344-426. Paper
14. (With H. Baik and T. Koberda), Unsmoothable group actions on compact one-manifolds, accepted, Journal of European Mathematical Society. Paper Summary
11. (With T. Koberda) Anti-trees and right-angled Artin subgroups of braid groups, Geometry & Topology 19-6 (2015), 3289--3306. Paper Summary



Current (Spring -- Fall 2017)

  • Sabbatical!


Lecture notes



  • Excellence in Research Award, College of Natural Sciences, Seoul National University, March 3, 2017.
  • Excellent Research Paper Award, Korean Mathematical Society, April 23, 2016.
For the work: (With Thomas Koberda), Embedability between right-angled Artin groups, Geometry & Topology 17 (2013) 493--530.
An award first established in September 2015. Based on recommendations by students council, faculty committee and course survey.
  • Creative Teaching Grand Award, KAIST, February 15, 2013.
  • Sang-San Prize for Young Mathematicians, Korean Mathematical Society, October 5, 2012.
  • Excellence Prizes, College Mathematics Competition, Korean Mathematical Society, 1994 and 1995.
  • Silver medal, the 34th International Mathematical Olympiad, Turkey, 1993.

Professional Services