Felix Klein’s Letters to Sophus Lie 1870–1877

This book provides an unparalleled combination of primary source material and critical analysis that fundamentally reinterprets the relationship between two mathematical pioneers. It opens with Klein's letters, which form the first two chapters, presented first in the original German and then in English translation, supported by comprehensive subject and name indexes as well as over 500 explanatory footnotes. Readers will follow the intense collaboration between Klein and Lie from 1869 to 1872, tracing their three joint publications and their individual development up to 1878. The later chapters examine how Klein's promotion of the Erlangen Program, his hesitant attitude toward Lie's work on the Riemann–Helmholtz space problem, and the so-called Killing affair shattered the bond between them. These chapters reveal how differing views on their achievements in the early 1870s, friction over continuous groups, and tensions surrounding Lie's nervous illness ultimately culminated in the final break between Klein and Lie in 1893. By uncovering these hidden conflicts and placing them in the context of major mathematical developments, the book bridges raw human drama with foundational ideas, making it essential reading for historians and mathematicians alike.