Post 1944: classify problems by relative-computability. Turing-jump A' = halting-problem-for-A. Friedberg-Muchnik 1956: incomparable r.e. degrees. Foundation of degree-theory.
Post 1944: classify problems by relative-computability. Turing-jump A' = halting-problem-for-A. Friedberg-Muchnik 1956: incomparable r.e. degrees. Foundation of degree-theory.