Turing, Alan M. (1936), “On Computable Numbers, with an Application to the Entscheidungsproblem”, Proceedings of the London Mathematical Society, 2 42 (1): pp. 230–65, 1937, doi:10.1112/plms/s2-42.1.230 (and Turing, Alan M. (1938), “On Computable Numbers, with an Application to the Entscheidungsproblem: A correction”, Proceedings of the London Mathematical Society, 2 43 (6): pp. 544–6, 1937, doi:10.1112/plms/s2-43.6.544)