Rudolf Halin

Rudolf Halin was a German graph theorist, known for defining the ends of infinite graphs, for Halin's grid theorem, for extending Menger's theorem to infinite graphs, and for his early research on treewidth and tree decomposition. He was born on February 3, 1934 in Uerdingen, earned his doctorate from the University of Cologne in 1962 under Klaus Wagner and Karl Dörge, and then joined the faculty of the University of Hamburg. He is also the namesake of Halin graphs, a class of planar graphs constructed from trees by adding a cycle through the leaves of the given tree; earlier researchers had studied the subclass of cubic Halin graphs, but Halin was the first to study this class of graphs in full generality. He died in Mölln, Schleswig-Holstein, on November 14, 2014.