Combinatorics (Topological Graph Theory, Enumeration), Combinatorial Topology

1973~1986 Associate professor of mathematics at Kyungpook National University's College of Natural Sciences.
1985~1986 Visiting professor of mathematics at the University of Michigan.
1986~2010 Associate professor of mathematics, Professor (currently Honorary professor)
1990~1992 POSTECH The dean of student director.
1992 A visiting professor of mathematics at Cambridge University in the U.K.
1994~1996 POSTECH, The head of the school affairs department.
1997~1998 Columbia University computer science department Visiting Professor
1999~2010 Designated by the Korea Science Foundation. Computerized Mathematics Research Center (SRC) Director
2000~ Canada, Institute of Combinatorics and its Application, Fellow
2004 Visiting Professor of Mathematics at Tsinghua University in China.
2011 ~ A chair professor at the Department of Mathematics at Beijing Jiaotong University in China.
2013 ~ Beijing Jiaotong University in China. Director of the Institute for Combination and Optimization.
2015 ~ Beijing Jiaotong University in China. Dean of Hanergy School of Renewable Energy
2015 ~ Chairman of KSEACH

2001 Academic Award of the Korean Mathematical Society.
2007 Achievement Award from the Korean Mathematical Society.
2010 Order of National Security Merit
2010 Top Cited Article 2005-2010. Awarded from Elsevier, The Netherlands
2014 Chinese Government Friendship Award