The Gallai Theorem

The Gallai Theorem is one of my favorite results in all of mathematics. Surprisingly, it is not widely known even among mathematicians. Its creator was Tibor Gallai, born Tibor Grünwald, a member of the Hungarian Academy of Sciences, who passed away on January 2, 1992, at the age of 79. His lifelong close friend and co-author Paul Erdős was staying me in Colorado Springs when Professor Vera T. Sós called from Budapest to give Paul the sad news of Gallai’s passing. Right then I asked Paul to write about Gallai for Geombinatorics. Here is Paul’s Obituary of My Friend and Coauthor Tibor Gallai [E92.14] in its entirety, including the sketch for the Sylvester–Gallai result that Paul drew on the margin of his manuscript.