English
For any Fin n and NeZero m, the image of Ioi i under castAddEmb m equals Ioo (castAdd m i) (natAdd n 0).
Русский
При любом i и не нулевом m образ Ioi i под castAddEmb m равен Ioo (castAdd m i) (natAdd n 0).
LaTeX
$$$ (\mathrm{Finset}.Ioi\, i).image (\mathrm{Fin.castAddEmb}\, m) = \mathrm{Finset}.Ioo\ (\mathrm{Fin.castAdd}\, m\, i) (\mathrm{Fin.natAdd}\, n\, 0) $$$
Lean4
@[simp]
theorem map_castAddEmb_Ioi (m) [NeZero m] (i : Fin n) : (Ioi i).map (castAddEmb m) = Ioo (castAdd m i) (natAdd n 0) :=
by simp [← coe_inj]