English
For a fixed c, Tendsto of the distance from f x to c to atTop is equivalent to Tendsto f to cobounded.
Русский
Для фиксированного c эквивалентны Tendsto расстояния до c к atTop и Tendsto самой функции к cobounded.
LaTeX
$$$\operatorname{tendsto}_{l} (\lambda x \mapsto \operatorname{dist}(f x, c)) \; \text{atTop} \iff \operatorname{Tendsto} f \; l \; (\operatorname{cobounded}(\alpha))$$$
Lean4
@[simp]
theorem tendsto_dist_right_atTop_iff (c : α) {f : β → α} {l : Filter β} :
Tendsto (fun x ↦ dist (f x) c) l atTop ↔ Tendsto f l (cobounded α) := by
rw [← comap_dist_right_atTop c, tendsto_comap_iff, Function.comp_def]