*Cheeger-Gromov $L^2$ rho-invariants and low dimensional**topology*, MFO workshop: Interactions between Low-dimensional Topology and Complex Algebraic Geometry, October 23, 2017, Oberwolfach, Germany.*Milnor invariants and rational Whitney towers*, September 25, 2017, St. Petersburg State University, St. Petersburg, Russia.

*Hirzebruch-type invariants of Cheeger-Gromov and low dimensional topology*, Oberseminar at Max Planck Institute for Mathematics, August 31, 2017, Bonn, Germany.*Bordism, chain homotopy, and Cheeger-Gromov $\rho$-invariants*, Quantitative Geometry and Topology — a special session in Mathematical Congress of America 2017, July 25, 2017, Montreal, Canada.- 다양체의 위상수학과 디스크 임베딩 (
*Topology of manifolds and disk embedding*), 무은재 석좌교수 기념강연 (Mueunjae Chair Professor Lecture), May 22, 2017, POSTECH, Pohang, Korea. *Whitney towers in a rational homology ball*, Invariants in Low-dimensional Topology, May 12, 2017, KIAS, Seoul, Korea.*Milnor invariants and rational Whitney towers*, April 19, 2017, Indiana University, Bloomington, Indiana, USA.*$L^2$-acyclic bordism and Whitney towers*, The 12th East Asian School of Knots and Related Topics, February 14, 2017, University of Tokyo, Japan.*Disk embedding in dimension four*, The 2nd KAST and Lincei bilateral symposium, December 6, 2016, Seoul, Korea.*Mathematics of dimension 4*, KAIST CMC Noon Lecture, December 2, 2016, KAIST, Daejeon, Korea.*A quantitative approach to Cheeger-Gromov rho invariants and 4-dimensional bordism*, October 25, 2016, Hausdorff Research Institute for Mathematics, Bonn, Germany.*4-dimensional $L^2$-acyclic bordism and Whitney towers*, Conference on 4-manifolds and knot concordance, October 17, 2016, Max Planck Institute for Mathematics, Bonn, Germany.*4-manifold topology and disk embedding*, Math Colloquium, October 6, 2016, Seoul National University, Seoul, Korea.*$L^2$-acyclic bordism groups of 3-manifolds*, Topology in Dimension 3.5: a conference in memory of Tim Cochran, June 4, 2016, Rice University, Houston, Texas, USA.*Complexity and Gromov norm of 3-manifolds*, International workshop of PMI, May 19, 2016, POSTECH, Pohang, Korea.*Quantitative topology and Cheeger-Gromov universal bounds*, April 27, 2016, Seoul National University, Seoul, Korea.

*Disk embedding in dimension 4*, Math Colloquium, March 17, 2016, KAIST, Daejeon, Korea.*A survey on topological concordance and disk embedding*, BIRS workshop: Synchronizing Smooth and Topological 4-Manifolds, February 22, 2016, Banff, Canada.*A topological approach to Cheeger-Gromov universal bounds of von Neumann rho invariants*, Geometry/Topology Seminar, February 18, 2016, University of Chicago, USA.*Casson towers, gropes, and disk embedding*, The 11th East Asian School of Knots and Related Topics, January 29, 2016, Osaka City University, Japan.*Controlled chain homotopy and von Neumann rho-invariants of Cheeger and Gromov*, East Asian Conference on Algebraic Topology, December 3, 2015, NIMS, Daejeon, Korea.*Complexities of 3-manifolds*, Knots and Spatial Graphs 2015, November 6, 2015, KAIST, Daejeon, Korea.*Topology of dimension 4 and disk embedding*, Math Colloquium, May 22, 2015, Ajou University, Suwon, Korea.

*Von Neumann-Cheeger-Gromov rho invariants and topology of 3-manifolds,*The 10th East Asian School of Knots and Related Topics, January 28, 2015, East China Normal University, Shanghai, China.*Topological manifolds of dimension 4 and disk embedding*, Math Colloquium, November 27, 2014, Konkuk University, Seoul, Korea

*Cheeger-Gromov universal bounds of von Neumann L2 rho-invariants*, Algebraic Structures in Low-Dimensional Topology, May 26, 2014, Mathematisches Forschungsinstitut Oberwolfach, Germany.*A new approach to Cheeger-Gromov universal bounds of L2 rho invariants*, March 18, 2014, Brandeis University, Waltham, Massachusetts, USA.

*A topological approach to Cheeger-Gromov universal bounds*, March 5, 2014, Indiana University, Bloomington, Indiana, USA.

*Universal bounds for the Cheeger-Gromov rho-invariants*, February 28, 2014, University of Wisconsin, Madison, Wisconsin, USA.

*A topological viewpoint to Cheeger-Gromov rho invariants*, GAIA-Institute Fourier Joint Conference on Geometry, July 15, 2013, Pohang, Korea.*Universal bounds of Cheeger-Gromov invariants: a topological viewpoint*, February 4, 2013, Rice University, Houston, Texas, USA.*Covering link calculus and the bipolar filtration of links*, The 9th East Asian School of Knots and Related Topics, January 15, 2013, University of Tokyo, Tokyo, Japan.*Homology cobordism of 3-manifolds and lower central series*, December 4, 2012, Syracuse University, Syracuse, New York, USA.

*The bipolar filtration of topologically slice links*, AMS Fall Central Sectional Meeting, Special Session on Knot Theory and 4-manifolds, October 20, 2012, University of Akron, Akron, Ohio, USA.*Amenable L2-signatures and cobordism of knots and 3-manifolds*, October 11, 2012, Harvard University, Cambridge, Massachusetts, USA.*Homology cobordism and lower central series of 3-manifold groups*, October 10, 2012, Brandeis University, Waltham, Massachusetts, USA.

*Amenable L2-signatures and homology cobordism of 3-manifolds*, September 12, 2012, Indiana University, Bloomington, Indiana, USA.*Cobordism of knots and 3-manifolds,*International Conference of Honam Mathematical Society, June 15, 2012, Jeju National University, Jeju, Korea.*Some recent results on links, 3-manifolds, Whitney towers and amenable Cheeger-Gromov invariants*, Tokyo workshop on low dimensional topology, March 20, 2012, Tokyo Institute of Technology, Tokyo, Japan.*Hidden torsion in 3-manifold groups and homology cobordism*, The 8th East Asian School of Knots and Related Topics, January 11, 2012, Daejeon, Korea.

*An introduction to $L^2$-invariants I, II, III*, The 8th East Asian School of Knots and Related Topics, January 9-11, 2012, Daejeon, Korea.*Invariants of cobordism of knots and 3-manifolds*, Invited talk at 2011 Fall Meeting of Mathematical Society of Japan, September 28, 2011, Shinshu University, Matsumoto City, Nagano, Japan.

*Whitney towers, knot concordance, and amenable L2-theoretic methods*, International Conference in Memory of Hyo Chul Myung, April 27, 2011, Seoul, Korea.*Homology localization of groups, injectivity theorems, and amenable L2-homological methods*, The 1st Euro-Korean Conference on Groups and Related Topics, March 30, 2011, Pohang, Korea.*Knots in dimension 3 and topology of dimension 4*, Math Colloquium, KAIST, March 24, 2011, Daejeon, Korea.*Applications of covering link calculus*, Topology Seminar, Indiana University, February 09, 2011, Bloomington, Indiana, USA.*Signatures of manifolds and knots*, 2011 Winter Workshop for Young Mathematicians in Korea, January 28, 2011, Pohang, Korea.*Whitney towers and Amenable L2-techniques*, The 7th East Asian School of Knots and Related Topics, Hiroshima University, January 13, 2011, Hiroshima, Japan.*Amenable L2-theoretic methods for knots and 3-manifolds*, Topology Seminar, Seoul National University, October 21, 2010, Seoul, Korea.*L2-signatures: twisted invariants from duality*, RIMS Seminar, Twisted topological invariants and topology of low-dimensional manifolds, September 17, 2010, Akita, Japan.*Why is the twisted Alexander polynomial related to fiberability?*RIMS Seminar, Twisted topological invariants and topology of low-dimensional manifolds, September 15, 2010, Akita, Japan.*L2-signatures and homology cobordism of 3-manifolds*, Lecture series on L2-invariants of knots and manifolds, August 11-13, 2010, KIAS, Seoul, Korea.*Homological L2-invariants of knots and manifolds I, II, III*, Lecture series on L2-invariants of knots and manifolds, August 11-13, 2010, KIAS, Seoul, Korea.*Amenable L2-theoretic methods and applications to knots and 3-manifolds*, The 2nd TAPU-KOOK Joint Seminar, July 30, 2010, Kyungpook National University, Daegu, Korea.*Introduction to L2-invariants*, Knot Concordance and Homology Cobordism Workshop, July 23, 2010, Wesleyan University, Middletown, Connecticut, USA.*Amenable L2-theoretic methods and applications*, Knot Concordance and Homology Cobordism Workshop, July 22, 2010, Wesleyan University, Middletown, Connecticut, USA.*Homology and L*, The 6th East Asian School of Knots and Related Topics, January 27, 2010, Chern Institute of Mathematics, Tianjin, China.^{2}-signatures from amenable groups*L*, Special Session on Knot Theory and Related Topics, Joint Meeting of the Korean Mathematical Society and the American Mathematical Society, December 18, 2009, Seoul, Korea.^{2}-signature defects and amenable groups*L*, International Conference on Symplectic, Contact and Low Dimensional Topology, November 12, 2009, Seoul, Korea.^{2}-signatures, homology, and amenable groups*Links in dimension 3 and their deformation in dimension 4*, Chonbuk National University, September 24, 2009, Jeonju, Korea.*Torsion in link concordance and Hirzebruch-type invariants from iterated p-covers*, Canadian Mathematical Society Summer Meeting, June 7, 2009, St. John’s, Newfoundland, Canada.*Links and intersection form defects*, Mathematical Colloquium, Seoul National University, May 14, 2009, Seoul, Korea.*The structure of the rational concordance group of knots*, Excellent Research Paper Award Lecture, 2009 Spring Meeting of the Korean Mathematical Society, April 25, 2009, Suwon, Korea.*Links in 3-space and their deformation in 4-space*, Mathematical Colloquium, Yonsei University, April 9, 2009, Seoul, Korea.*Local derived series, L2-signatures, and applications to manifolds*, The 5th East Asian School of Knots and Related Topics, January 13, 2009, Gyeongju, Korea.*Using Artin reciprocity in knot theory*, Kyushu-POSTECH joint workshop on number theory and related topics, January 6, 2009, Pohang, Korea.*Deformation of links in dimension 4*, Mathematical Colloquium, Chungang University, November 21, 2008, Seoul, Korea.*4-dimensional deformation of links in the 3-space*, Mathematical Colloquium, Sogang University, October 9, 2008, Seoul, Korea.*Slicing and non-slicing iterated Bing doubles*, Topology-Geometry Seminar, Indiana University, August 26, 2008, Bloomington, Indiana, USA.*Link concordance, homology cobordism, and iterated p-covers*, Fifty years since Fox and Milnor: a conference on knot concordance in honor of the memory of Jerry Levine, Brandeis University, June 3, 2008, Waltham, Massachusetts, USA.*Link concordance and Hirzebruch-type invariants from iterated covers*, Pusan Nation University, April 18, 2008, Pusan, Korea.*Slicing iterated Bing doubles*, a plenary talk at The 4th East Asian School of Knots and Related Topics, January 21, 2008, Tokyo, Japan.*Non-slice iterated Bing doubles*, Topology Seminar, UC Berkeley, November 14, 2007, Berkeley, California, USA.*Homology, injectivity theorems, and algebraic closures with coefficients*, East Asian Conference of Algebraic Topology, November 3, 2007, Seoul, Korea.*New Hirzebruch-type invariants from iterated p-covers*, The 7th KAIST Geometric Topology Fair, July 9, 2007, Gyeongju, Korea.*An elementary tutorial on provable security*, KIAS-KMS Summer workshop on Cryptography, June 29, 2007, Seoul, Korea.*Invariants of homology cobordism and link concordance from towers of itrated abelian p-covers*, Geometric Topology Conference, Peking University, June 19, 2007, Beijing, China.*The structure of the rational knot concordance group*, Department of Mathematics, POSTECH, May 23, 2007, Pohang, Korea.*Introduction to Geometric Topology and Knot Theory*, Departmental Colloquium, Department of Mathematics, Konkuk University, April 13, 2007, Seoul, Korea.*Hirzebruch-Atiyah-Singer type invariants of manifolds and applications to knot theory*, Department of Mathematics, Ewha Womans University, March 30, 2007, Seoul, Korea.*Witt class defect invariants, homology cobordism, and link concordance*, a talk at The Third East Asian School of Knots and Related Topics in Geometric Topology, February 6, 2007, Osaka, Japan.*Classifications of manifold embeddings*, Mathematical Colloquium, Korea Institute for Advanced Study, November 22, Seoul, Korea.*Invariants from Atiyah-type theorems and applications to links*, an invited talk at 2006 Geometry & Topology Day at Konkuk University, November 18, 2006, Seoul, Korea.*Homology equivalences, injectivity theorems, and algebraic closures of groups*, an invited talk at NIMS Workshop on Geometry and Topology, November 16, 2006, Daejeon, Korea.*The structure of the concordance group of knots in rational homology spheres*, an invited talk at 2005 fall meeting of the Korean Mathematical Society, 21 October, 2005, Seoul, Korea.*Algebraic closures with coefficients and torsion-free derived series*, a plenary talk at The Second East Asian School of Knots and Related Topics in Geometric Topology, August 4, 2005, Dalian, China.*Algebraic closures with coefficients and applications to homology cobordism*, January 31, 2005, Department of Mathematics, Rice University, Houston, Texas, U.S.A.*Homology equivalences and algebraic closures*, January 24, 2005, Department of Mathematics, Indiana University, Bloomington, Indiana, U.S.A.*Classification of knots from the viewpoint of manifold theory*, November 25, 2004, Department of Mathematics, Konkuk University, Seoul, Korea.*Classification of knots from the viewpoint of manifold theory*, November 4, 2004, Department of Mathematics, Ewha Womans University, Seoul, Korea.*Torsion-free derived series, algebraic closures, and link concordance*, The First KAIST Geometric Topology Fair, August 25, 2004, Chungju, Korea.*Randomized computation and provable security I, II*, Korea Institute for Advanced Study, August 6-7, 2004, Seoul, Korea.*Rational homology concordance of knots*, BIRS Workshop on Knots and Their Manifold Stories, May 11, 2004, Banff, Alberta, Canada.*Provable security of ID-based cryptosystems*, National Security Research Institute, March 11, 2004, Daejeon, Korea.*Concordance of knots in rational homology spheres*, The First East Asian School of Knots, Links, and Related Topics, February 17, 2004, Seoul, Korea.*Localization, surgery and placement problems of manifolds*, Departmental Colloquium, Department of Mathematics, Korea Advanced Institute of Science and Technology, December 4, 2003, Daejeon, Korea.*Concordance and rational knots*, Korea Advanced Institute of Science and Technology, March 27-28, 2003, Daejeon, Korea.*The structure of the rational knot concordance group*, AMS special session, March 14, 2003, Baton Rouge, Louisiana, U.S.A.*The effect of mutation on link concordance, 3-manifolds, and the Milnor invariants*, AMS special session, January 17, 2003, Baltimore, Maryland, U.S.A.*Concordance and rational knots*, Knots in Washington XV, January 10, 2003, Washington, DC, U.S.A.*Computation of rational knot concordance*, October 8, 2002, Brandeis University, Waltham, Massachusetts, U.S.A.*A survey on link concordance*, January 15, 2002, Nara Women’s University, Nara, Japan.*Implementations of braid cryptosystems*, An invited tutorial in International Workshop on Practice and Theory in Public Key Cryptography, February 13, 2001, Cheju, Korea*Link concordance theory in rational homology spheres and its application to concordance of homology boundary links*, KNOTS 2000, August 2, 2000, YoungPyong, Kangwon, Korea.