  One person who knew Ketonen's calculus in the late 1940s was Evert  Beth. When Beth later, in 1955, presented his well-known tableau  calculus, he seems to have forgotten the origin of the tableau  calculus as a reformulation of the one of Ketonen, but refers instead to Kleene's influential Introduction to Metamathematics of  1952. Kleene had taken up Ketonen's calculus from the Bernays' review  and also treated intuitionistic sequent calculus in which  invertibility is more restricted than in the classical calculus. With Kleene's book, Gentzen's sequent calculi became generally known and  accessible.