Professor Evgenii Mikhailovich Landis

In 1946, Aleksandr Kronrod and Landis reinvented Sard's Lemma that was unknown in Moscow at the time. (During the war, scientific exchanges were non-existent.) For a while, Sard's Lemma was called the Kronrod-Landis Theorem in Russian papers. Landis wrote several papers in Real Analysis. He proved an analogue of Sard's Lemma for a difference of two convex functions, with no conditions on their smoothness imposed. He found the complete characterization of sets where a continuous function on an interval has infinite derivative. Landis's background in Real Analysis can be felt in all his future works. Later he worked on uniqueness theorems for elliptic and parabolic differential equations, Harnack inequalities, and Phragm?n?Lindel?f type theorems. With Georgy Adelson-Velsky, he invented the AVL tree datastructure (where "AVL" stands for Adelson-Velsky Landis).