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computable sets and functions, Turing degrees, c.e. degrees, models of computability, primitive recursion, oracle computation, models of computability, decision problems, undecidability, Turing jump, halting problem, notions of computable randomness, computable model theory, computable equivalence relation theory, arithmetic and hyperarithmetic hierarchy, infinitary computability, $\alpha$-recursion, complexity theory.

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Why is every finite set Diophantine?

Or, very simply stated, given the finite set $S = \{a_1, \dots , a_k\}$, consider the diophantine equation: $$(n-a_1)\dots(n-a_k)=0.$$ EDIT: Then we can write S as $\{ \ n \ | \ \exists x : (n-a_1)\do …
Emil Jeřábek's user avatar