English
Applying ofFin to a Fin2 element obtained from toFin yields the original Fin2 element.
Русский
Применение ofFin к Fin2-элементу, полученному из toFin, возвращает исходный Fin2-элемент.
LaTeX
$$$\mathrm{Fin2\text{-}ofFin}(\mathrm{toFin}(i)) = i.$$$
Lean4
@[simp]
theorem ofFin_toFin {n : Nat} (i : Fin2 n) : ofFin (toFin i) = i := by
induction i with
| fz => rfl
| fs _ ih => exact congrArg fs ih