Lange also made contributions in various other areas. He was one of the leading lights of the "Paretian Revival" in general equilibrium theory during the 1930s. In 1942, he provided one of the first proofs of the First and Second Welfare Theorems. He initiated the analysis of stability of general equilibrium (1942, 1944). His critique of the quantity theory of money (1942) prompted his student Don Patinkin to develop his remarkable "integration" of money into general equilibrium theory. Lange made several seminal contributions to the development of neoclassical synthesis (1938, 1943, 1944). He worked on integrating classical economics and neoclassical economics into a single theoretical structure (e.g. 1959). In his final years, Lange also worked on cybernetics and the use of computers for economic planning.