This man's eponymous lemm
This man's eponymous lemma is used to directly prove the Riemann mapping theorem, and one variant of that lemma states that any analytic map from the unit disk to itself that preserves hyperbolic distance between any two points will preserve distance between all points, and is also named for Georg Pick. His transformation takes the upper half z-plane to the interior of a simple closed polygon, and is also named for Christoffel, while his reflection principle is used in extending domains in analytic continuation. FTP, name this ►German mathematician, who lent his name to a type of spherical triangle and developed an inequality relating the norms of two vectors to the norm of the sum of the vectors independently of Cauchy.
This man's eponymous lemma is used to directly prove the Riemann mapping theorem, and one variant of that lemma states that any analytic map from the unit disk to itself that preserves hyperbolic distance between any two points will preserve distance between all points, and is also named for Georg Pick.
Hermann Amandus {Schwarz}