finsetImage_cast_Ici — Mathlib

English

Let h be a natural equality h: n = m and i ∈ Fin n. The image of the interval Ici(i) under Fin.cast h is Ici(i.cast h).

Русский

Пусть h : n = m и i ∈ Fin n. Образ множества Ici(i) при приведении Fin.cast h равен Ici(i.cast h).

LaTeX

$$$$ \operatorname{Finset.image}(\operatorname{Fin.cast} h)(\operatorname{Finset.Ici}(i)) = \operatorname{Finset.Ici}(\operatorname{Fin.cast} h\, i) $$$$

Lean4

@[simp]
theorem finsetImage_cast_Ici (h : n = m) (i : Fin n) : (Ici i).image (.cast h) = Ici (i.cast h) := by simp [← coe_inj]

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