 (3) is often considered (although not in fact by Kleene himself) to be very strong evidence for the thesis, because of the diversity of the various formal analyses involved. For example, apart from the analyses already mentioned in terms of lambda-definability and recursiveness—and, of course, Turing-machine computability—there are analyses in terms of register machines (Shepherdson and Sturgis 1963), Post’s canonical and normal systems (Post 1943, 1946), combinatory definability (Schönfinkel 1924; Curry 1929, 1930, 1932), Markov algorithms (Markov 1960), and Gödel’s notion of reckonability (Gödel 1936; Kleene 1952).