∀ {α : Type u_1} [inst : PseudoEMetricSpace α] (C : ENNReal) {f : ℕ → α},
  (∀ (n : ℕ), edist (f n) (f (n + 1)) ≤ C / 2 ^ n) →
    ∀ {a : α}, Filter.Tendsto f Filter.atTop (nhds a) → ∀ (n : ℕ), edist (f n) a ≤ 2 * C / 2 ^ n