Let `X` be the set of points in `Fin d → ℝ` of the shape
`fun i : Fin d => ∑' n : A, (1 : ℝ) / (n + i)` for some infinite subset `A ⊆ ℕ` such that
`1 / n` is summable over `A`. `X` has nonempty interior. This is proved in [KoTa24].
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theorem erdos_268 (d : ℕ) : (interior {x : Fin d → ℝ | ∃ A : Set ℕ, A.Infinite ∧
Summable (fun n : A => (1 : ℝ) / n ) ∧
x = fun i : Fin d => ∑' n : A, (1 : ℝ) / (n + i)}).Nonempty
