Consider with the Euclidean metric d. Let , and for any integer . Let X = ⋃, where is the line segment joining and O. Define as follows: d_X(a, b) = d(a, b) when for some n, and d_X(a, b) = d(a, O) + d(b, O) otherwise. Let be the smallest topology such that the sets {} are open in for all a ∈ X and . Which of the following statements are true?
Multi-select · full marks only for the exact set · Metric Spaces