Richard Bellman, The theory of dynamic programming, in Bulletin of the American Mathematical Society, vol. 60, n. 6, 1954, pp. 503-515, DOI:10.1090/S0002-9904-1954-09848-8.
Donald Michie, Memo functions and machine learning, in Nature, vol. 218, 1968, pp. 19-22, DOI:10.1038/218019a0.