English
IsTopologicalGroup structure on G is determined by nhds at 1; two structures are equal iff their nhds at 1 coincide.
Русский
Структура IsTopologicalGroup на G определяется через nhds в единице; равенство структур эквивалентно совпадению nhds(1).
LaTeX
$$$IsTopologicalGroup\;ext\_iff$$$
Lean4
@[to_additive]
theorem ext_iff {G : Type*} [Group G] {t t' : TopologicalSpace G} (tg : @IsTopologicalGroup G t _)
(tg' : @IsTopologicalGroup G t' _) : t = t' ↔ @nhds G t 1 = @nhds G t' 1 :=
⟨fun h => h ▸ rfl, tg.ext tg'⟩