Carsten Thomassen

Carsten Thomassen received his PhD in 1976 under the supervision of Daniel Younger. The title of his thesis is "Paths and Cycles in Graphs". Since 1981, he has been a Professor of Mathematics at the Technical University of Denmark.

Carsten has become one of the very top graph theorists in the world, with work spanning the entire gamut of the subject. He has made profound inroads in planarity, colourings of graphs, directed graphs, eigenvalues of graphs, flows in graphs, embeddings of graphs, and connectivity in graphs, to name a few. He has over 200 publications, with the vast majority occurring in top journals in combinatorics and, indeed, mathematics more generally.

Carsten has a well-earned reputation as being the master of mathematical induction. His celebrated proof that every planar graph is 5-list-colourable is a wonderful example of this; it is one of the simplest proofs of the (much weaker) 5-colour theorem known.

Besides being a prolific researcher, Carsten also has a keen appreciation for exposition in more general mathematical forums, such as the American Mathematical Monthly. His proof of the Jordan Curve Theorem demonstrates his mastery of topology and its interaction with graph theory.  

Carsten's insights showing the strong links between the Jordan Curve Theorem and the graph K(3,3) led to a surprising result. He characterizes the sphere as a compact, arcwise-connected, metric space in which the deletion of an arc leaves an arcwise-connected subspace, while the deletion of any simple closed curve leaves a disconnected subspace. The surprising aspect is that there is no need for any local properties, such as local-connection.

In 2005, Carsten received the Faculty of Mathematics Alumni Achievement Medal in recognition of his outstanding academic research career. He is the Chief editor of Journal of Graph Theory and Electronic Journal of Combinatorics. He was an invited speaker at the International Congress of Mathematicians in 1990, and received the 1993 Lester R. Ford Award from the Mathematical Association of America.