English
For any o, the composite ofOption ∘ toOption is the identity on Part: ofOption (toOption o) = o.
Русский
Для любого o, композиция ofOption ∘ toOption является тождественной на Part: ofOption (toOption o) = o.
LaTeX
$$$ \mathrm{ofOption}(\mathrm{toOption}(o)) = o $$$
Lean4
@[simp]
theorem of_toOption (o : Part α) [Decidable o.Dom] : ofOption (toOption o) = o :=
ext fun _ => mem_ofOption.trans mem_toOption