 Solution

ID: past-exam-of-the-topology-course-of-the-university-of-oxford/2015/2/a/i/solution

X = i \in I ⋃ U_{i}, U_{i} open ⟹ X = U_{i_{1}} \cup \dots \cup U_{i_{n}} for finitely many indices .

There is no Hausdorff requirement in this definition.

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