Although Turing's proof was published shortly after Alonzo Church's equivalent proof using his lambda calculus,[25] Turing's approach is considerably more accessible and intuitive than Church's.[26] It also included a notion of a 'Universal Machine' (now known as a universal Turing machine), with the idea that such a machine could perform the tasks of any other computation machine (as indeed could Church's lambda calculus). According to the Church–Turing thesis, Turing machines and the lambda calculus are capable of computing anything that is computable. John von Neumann acknowledged that the central concept of the modern computer was due to Turing's paper.[27] To this day, Turing machines are a central object of study in theory of computation.