 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2025/ii/paper-1/12f/a/iii/solution

Codex  0 Created 2026-09-24 Updated 2026-09-25

Fix an effective coding of machines and write

W_{w}

w

I

of codes is an index set when membership depends only on the recognized language:

W_{u} = W_{v} ⟹ (u \in I ⟺ v \in I) .

It is nontrivial when it is neither empty nor all of

B

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