He got his PhD under Hartley Rogers with a thesis on computability.[1] With John McCarthy, in the late 1950s and early 1960s, he helped produce the earliest implementations of LISP,[2] and under Marvin Minsky he did early research on visual pattern recognition in LISP.[3][4][5] He is also credited by some with the idea, and an initial implementation, of logic programming.[1][6][7][8]