Marx Brothers made a guest appearance to introduce the "Tonight Show's" new host, Johnny Carson. Around 1960, the acclaimed director Billy Wilder considered writing and directing a new Marx Brothers film. Tentatively titled "A Day at the U.N.", it was to be a comedy of international intrigue set around the United Nations building in New York. Wilder had discussions with Groucho and Gummo, but the project was put on hold because of Harpo's ill-health and abandoned when Chico died in 1961. He was 74. Three years later, on September 28, 1964, Harpo died at the age of 75 of a heart attack
Karl Marx and the Close of His System labour value, he argues that the basic error in Marx's system resulted from a self-contradiction of Marx's law of value, namely how the rate of profit and the prices of production of the third volume of Marx's "Capital" contradict Marx's theory of value in the first volume. He maintains that since the law of value is not directly controlling in capitalist production, the theory of value must be abandoned. Bawerk also attacks Marx for downplaying the influence of supply and demand in determining permanent price, and for deliberate ambiguity with such concepts. "Karl Marx and the Close of His System"