English
The reverse equivalence (E × (F × G)) ≃ ((E × F) × G) is smooth.
Русский
Обратное эквивалентное преобразование гладко.
LaTeX
$$$\operatorname{ContDiff}_{\mathbb{K}} n ((\mathrm{prodAssoc}\; E\; F\; G)^{\,-1})$$$
Lean4
/-- The natural equivalence `(E × F) × G ≃ E × (F × G)` is smooth.
Warning: if you think you need this lemma, it is likely that you can simplify your proof by
reformulating the lemma that you're applying next using the tips in
Note [continuity lemma statement]
-/
theorem contDiff_prodAssoc {n : WithTop ℕ∞} : ContDiff 𝕜 n <| Equiv.prodAssoc E F G :=
(LinearIsometryEquiv.prodAssoc 𝕜 E F G).contDiff