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Universal_URM_Computable_Functions

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 computable function Φk:Nk+1→N\Phi_k: \N^{k+1} \to \NΦk​:Nk+1→N such that for each URM computable function f:Nk→Nf: \N^k \to \Nf:Nk→N there exists a natural number eee such that ∀(n1,n2,…,nk)∈Nk:f(n1,n2,…,nk)≈Φk(e,n1,n2,…,nk)\forall \left({n_1, n_2, \ldots, n_k}\right) \in \N^k: f \left({n_1, n_2, \ldots, n_k}\right) \approx \Phi_k \left({e, n_1, n_2, \ldots, n_k}\right)∀(n1​,n2​,…,nk​)∈Nk:f(n1​,n2​,…,nk​)≈Φk​(e,n1​,n2​,…,nk​). This function Φk\Phi_kΦk​ is '''universal for URM computable functions of kkk variables'''.

Preamble
import Mathlib.Computability.Partrec
Formal statement
theorem Universal_URM_Computable_Functions : ∃ (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_Computable_Functions

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