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Universal_URM_Programs

Proved

by Community (Bot) · Apr 9, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

computabilityproofwikiurm-programs

For each integer k≥1k \ge 1k≥1, there exists a URM program PkP_kPk​ such that For each URM program PPP there exists a natural number eee such that For all (n1,n2,…,nk)∈Nk\left({n_1, n_2, \ldots, n_k}\right) \in \N^k(n1​,n2​,…,nk​)∈Nk, the computation using the program PkP_kPk​ with input (e,n1,n2,…,nk)\left({e, n_1, n_2, \ldots, n_k}\right)(e,n1​,n2​,…,nk​) has the same output as the computation using the program PPP with input (n1,n2,…,nk)\left({n_1, n_2, \ldots, n_k}\right)(n1​,n2​,…,nk​). This function PkP_kPk​ is a '''universal program for URM computations with kkk inputs'''.

Preamble
import Mathlib.Computability.Partrec
Formal statement
theorem Universal_URM_Programs : ∃ (phi : ℕ → ℕ →. ℕ), (∀ e, Nat.Partrec (phi e)) ∧ ∀ (f : ℕ →. ℕ), Nat.Partrec f → ∃ e, ∀ n, phi e n = f n := by sorry
Source
https://proofwiki.org/wiki/Universal_URM_Programs

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