On the collaboration of Felix Klein and Sophus Lie in the early 1870's, seen in the light of Klein's letters to Lie

Felix Klein and Sophus Lie, both professors in Leipzig in the 1880-90's, were among the most influential mathematicians during the last decades of the 19th century, and their ideas have had a profound impact on the development of modern mathematics through the 20th century. They happened to meet for the first time in Berlin in the fall 1869, at the very beginning of their careers. Despite their different personality, age, and educational background, they developed a close friendship and shared a deep interest in geometry, which resulted in an intense collaboration and exchange of ideas during the following three years 1870-72. Moreover, their friendship and vivid letter correspondence continued for two more decades. Unfortunately, from their correspondence prior to 1878 only the letters from Klein to Lie have survived, but they will be published in the nearest future. In this talk we shall primarily focus on the circumstances leading to their close friendship and collaboration through 1869-72, seen in the light of these letters.