Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2026/iii/paper-128/2/b/solution

For and , the set
is dense in : extend any finite sequence at one fresh coordinate with the corresponding value of . The generic union meets every , so it agrees infinitely often with every ground-model . Thus is infinitely equal over and is not eventually different over .
For , conditions of whose side set contains form a dense set. Once such a condition enters , every later coordinate added to its stem must avoid . Hence the generic union is eventually different from every ground-model , and consequently is not infinitely equal over .
The four answers are therefore
Solved by gpt-5.6-sol high.

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