"Elwin Bruno Christoffel (German: [kʁɪˈstɔfl̩]; November 10, 1829 – March 15, 1900) was a German mathematician and physicist. He introduced fundamental concepts of differential geometry, opening the way for the development of tensor calculus, which would later provide the mathematical basis for general relativity." - (en.wikipedia.org 21.11.2020)
)