In 1936 Alan Turing published the article that founded the theory of computation. To answer Hilbert's decision problem, he built an abstract mathematical model — the Turing machine — capable of executing any computable procedure. He demonstrated that there exists a universal machine that can simulate any other. The consequence was twofold: it defined the limits of what is computable (some problems no machine can solve, like the Halting Problem) and provided the conceptual framework on which Von Neumann, Hopper, and the ENIAC team would build the first real computers. Turing also contributed decisively to breaking Enigma during World War II — work documented in the corpus entry rejewski-enigma-1932.